OCC/PartDesign: Pockets into Ellipse do weird things

Problem description

I am unable to make a pocket into an Elliptical body without weird glitches that break the whole model. Recomputing doesnt help. This seems to affect all subtractive tools.

Workbench affected?

Part Design

Steps to reproduce

Here is a copy of the file I am working on: test for freecad issue.zip (rename extension from .zip to .FCStd)

1. attempt to create a 5mm pocket with Sketch 9.
2. observe error message claiming no material is removed (the first problem: material is clearly being removed)
3. click "OK" for a 5mm pocket
4. observe wacky glitches like this:

Expected behavior

I would expect that the pocket would succeed and that the final result would reflect the appropriate pocket as defined by the sketch.

Actual behavior

See above screenshot

See for yourself :)

Development version About Info (in Safe Mode)

OS: Artix Linux (KDE/plasma/wayland)
Architecture: x86_64
Version: 1.2.0dev.20260421 (Git shallow) AppImage
Build date: 2026/04/21 23:21:45
Build type: Release
Branch: (HEAD detached at 449725202)
Hash: 449725202d0ab581516aacad59d62cdce80db82a
Python 3.11.14, Qt 6.8.3, Coin 4.0.8, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.2, OCC 7.8.1
Locale: English/United States (en_US)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Object center
Logical DPI/Physical DPI/Pixel Ratio: 96/95.3468/1.44792

Last known good version (optional)