[Bug] Multiline paste confirmation dialog applies an incorrect light overlay to specific Terminal windows #20853

Windows Terminal version

1.25.2733.0

Windows build number

10.0.26200.0

Other Software

PowerShell 7.6.7 and 7.6.8 (tested during troubleshooting)

Herdr: terminal-based multi-agent workspace UI. The issue also reproduces in plain PowerShell without Herdr.

clippath: a clipboard utility that monitors clipboard updates. The issue still reproduces after stopping the watcher and replacing clipboard contents with ordinary multiline text.

No third-party application has been confirmed as the cause.

Steps to reproduce

Reproduction steps

The initial trigger is unknown. However, once a Windows Terminal window enters the affected state, the issue can be reproduced consistently.

1. Open Windows Terminal with the dark theme.
2. Copy ordinary multiline text to the clipboard, for example:

Set-Clipboard -Value "FIRST LINE`nSECOND LINE`nTHIRD LINE"

3. Press Ctrl+V in the affected Terminal window.
4. Leave the multiline paste confirmation dialog open.
5. Observe the unexpectedly bright gray/white background behind the dialog.
6. Open a separate Terminal window using wt -w new and repeat the same test. The new window displays the normal dark background.

Troubleshooting performed

• Same Windows Terminal version and configuration in affected and unaffected windows.
• Reproduced with plain PowerShell, without Herdr.
• Reproduced after opening new tabs and replacing/splitting panes in the affected window.
• Reproduced again after a Windows reboot.
• Ctrl+Shift+MouseWheel opacity adjustments did not resolve the issue.
• Changing the PowerShell background image opacity to zero did not resolve the issue.
• "experimental.rendering.forceFullRepaint": true did not resolve the issue.
• Switching windows with Alt+Tab did not resolve the issue.
• The command palette (Ctrl+Shift+P) displayed normally.
• Stopping the clippath watcher and copying fresh, ordinary text did not resolve the issue.
• A newly launched elevated Terminal window displayed normally, so elevation alone does not appear sufficient to trigger the bug.

Window-style comparison

Both tested sessions reported:

ExStyle: 0x08200080
Layered: False
Transparent: False

These values were obtained through GetConsoleWindow() and may not describe the actual top-level Terminal UI windows.

Reproducibility

Consistently reproducible in affected window instances, but not in all newly created windows. The initial trigger remains unknown.

Expected Behavior

The multiline paste confirmation dialog should consistently dim the background using the appropriate dark-theme appearance.

All Terminal windows using the same theme and configuration should display a visually consistent modal background overlay, regardless of the shell, tab, pane layout, or whether the window was created earlier or more recently.

Actual Behavior

Some Windows Terminal windows display an unexpectedly bright gray/white overlay behind the multiline paste confirmation dialog.

Depending on the affected window and layout, the brightness can cover the entire window or appear unevenly, with some rectangular regions remaining dark.

The confirmation dialog itself stays dark, while the tab bar, terminal content, and background images may appear significantly brighter.

Newly created Terminal windows using the same configuration behave normally. The issue also recurred after rebooting Windows.

The behavior appears to be associated with individual top-level Terminal window instances rather than specific PowerShell panes.

The exact initial trigger and root cause have not yet been identified.

Screenshots and test conditions

The following screenshots document the visual issue under different conditions. The initial trigger remains unknown, but the behavior is reproducible in affected Terminal windows.

Figure 1 — Affected versus unaffected Terminal windows

Two Windows Terminal windows are shown side by side. The affected window on the left displays an unexpectedly bright gray background when the multiline paste confirmation dialog appears, while the separate window on the right retains its normal dark appearance.

This demonstrates that the issue does not occur consistently across Terminal windows using the same application version and configuration.

Figure 2 — Issue persists after stopping clippath

The clipboard utility was stopped using clippath stop, and fresh multiline text was copied using Set-Clipboard.

The affected Terminal window still displays the bright backdrop behind the confirmation dialog. The right-hand window shows that the clipboard watcher was stopped.

This suggests that an actively running clippath watcher is not required to reproduce the issue.

Figure 3 — Issue persists in newly created split panes

The affected Terminal window was kept open while new PowerShell panes were created.

Both panes display the same unexpectedly bright modal backdrop, even without the Herdr interface.

This suggests that the issue is associated with the Terminal window instance rather than an individual PowerShell pane or terminal application.

Figure 4 — Normal behavior in a newly launched elevated window

A new Windows Terminal window was launched with administrator privileges.

The multiline paste confirmation dialog appears with the expected dark background, unlike the affected windows.

This indicates that elevation alone is not sufficient to trigger the issue.

Figure 5 — Uneven overlay coverage in a split layout

An earlier affected Terminal window contained a more complex pane layout, including the Herdr terminal interface.

When the multiline paste confirmation dialog appeared, large portions of the window became light gray, while some rectangular regions remained dark.

This illustrates that the unexpected overlay may affect different regions of the same window inconsistently.

Summary: The screenshots suggest a window-instance-specific issue involving the multiline paste dialog's background treatment. The underlying cause and the event that initially triggers the affected state have not yet been identified.