Interior Corner bug

[rmu75]

Describe your issue

Interior corners don't mix with "material inside" or "thickness outside" (see screenshots). It seems if the base plate needs to be shrunk the edge is extended through the whole plate.

example (rename to .FCStd)
sminteriorcornerbug.zip

FreeCAD version info + SheetMetal WB version

OS: KDE neon User Edition (KDE/plasma/wayland)
Architecture: x86_64
Version: 1.1.1.20260414 (Git shallow) AppImage
Build date: 2026/04/14 22:09:59
Build type: Release
Branch: (HEAD detached at 0108fd4b4)
Hash: 0108fd4b4850cc46e625b60e53cea7a7bbe69f8d
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, 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 0.8.4, OCC 7.8.1
Locale: German/Austria (de_AT)
Navigation Style/Orbit Style/Rotation Mode: Touchpad/Trackball/Drag at cursor
Stylesheet/Theme/QtStyle: OpenLight.qss/OpenLight/
Logical DPI/Physical DPI/Pixel Ratio: 96/113.876/1.39583
Installed mods: 
  * btl 0.9.9
  * Gridfinity 0.12.4
  * kicadStepUpMod 11.8.7
  * dodo 1.0.1
  * OpticsWorkbench 1.3.7
  * OpenTheme 2025.5.20
  * Assembly3 0.12.3
  * frame 0.1.1
  * sheetmetal 0.8.21
  * FeedsAndSpeeds 0.6.0
  * offline-documentation 1.0.0-alpha
  * InventorLoader 1.5.1
  * EM 2.1.1

Put here any screenshots or videos (optional)

No response

[shaise]

Yes, Material inside does not play well with objects containing concave corners.
In this case I would suggest manually reducing the bottom plate dimensions, and use the more reliable material outside