DATA LOSS: "Edit Position" button erases entire move data from PGN!

[ed-cetera]

Describe the bug

When opening a PGN file containing move data (including possible variations) and clicking on the "Edit position" button in the chessboard interface, all move data is erased from the PGN. In some cases, this happens only after making an edit to the position—even if the edit is undone before closing the edit interface. Since the changes are written directly to the underlying file and there is no undo option, the data is lost permanently. A screenshot is attached, highlighting the button in question.

Reproduction

⚠ WARNING: Trying to reproduce this issue may result in permanent data loss. Ensure you have a backup or are using a test file before proceeding.

1. Open or create a PGN file containing move data.
2. Click on the "Edit position" button in the chessboard interface (see screenshot). In some cases, the move data is deleted immediately; in others, making an edit to the position (even if undone before closing the edit interface) triggers the deletion.
3. Observe that all move data has been deleted.

Platform and versions

macOS Sequoia 15.3.1 (24D70)
En Croissant 0.11.1 (same behavior with En Croissant developer version built from current master branch 85394a1)