std::bad_cast when reopening Shift Times with pt_BR locale after saving frame-based history (migration03)

[Jef295]

Summary

A std::bad_cast exception occurs when reopening Timing → Shift Times while using the Português (Brasil) (pt_BR) locale.

The crash is reproducible only after the dialog has been used to perform a frame-based shift greater than one frame. It does not occur when shifting by time.

This appears to be similar to issue #211, although the reproduction steps are different.

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Environment

Executable

• Aegisub-9794-migration03

Operating System

• Windows 10 Pro 22H2

UI language

• Português (Brasil) (pt_BR)

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Steps to reproduce

1. Delete shift_history.json.
2. Start Aegisub.
3. Open Timing → Shift Times.
4. Under Shift by, select Frames.
5. Enter a value greater than 1 (for example, 2).
6. Click OK.
7. Close the Shift Times dialog.
8. Open Timing → Shift Times again.

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Actual result

Aegisub throws:

std::bad_cast

and the dialog cannot be opened.

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Expected result

The Shift Times dialog should reopen normally.

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Additional observations

• Shifting by 1 frame does not reproduce the issue.
• Shifting by time does not reproduce the issue.
• Deleting shift_history.json restores normal behavior until another frame-based shift (>1 frame) is saved.

Once the crash starts occurring:

• pt_BR → ❌ Shift Times always crashes.
• Switching the UI language to pt_PT (or another tested locale) → ✅ Shift Times opens normally.
• Switching back to pt_BR without changing anything else → ❌ the crash immediately returns.

The executable, configuration, and shift_history.json remain exactly the same throughout these tests; only the selected UI language changes.

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Investigation

All tests were performed using the same executable (Aegisub-9794-migration03).

Only the translation catalog or the selected UI language was changed.

Translation	Result
Original pt_BR	❌ Crash
pt_PT	✅ Works
Other tested locales	✅ Work correctly
Modified pt_BR (plural entries removed)	✅ Works
Modified pt_BR (all translation entries preserved, workaround applied)	✅ Works

The workaround that avoids the crash displays the Shift Times history as:

Sem título, 10 frames trás, i+f, todas
Sem título, 3 frames trás, i+f, todas
Sem título, 2 frames trás, i+f, todas

Only the word "frames" remains untranslated; the rest of the history entry is still displayed in Portuguese.

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Additional information

The same original pt_BR/aegisub.mo that consistently reproduces this issue on Aegisub-9794-migration03 does not reproduce the issue when used with:

• Aegisub-9820-cibuilds-8165f1ad5

This report is specifically about the migration03 build. The comparison above is provided only as additional information.

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Related issue

Possibly related to #211:

Crash (std::bad_cast) when opening "Shift Times" with zh_TW locale on migration03-02.