The steps to reproduce:
- Switch to Part wb and create a document
- Create a Part container and a box
- Move the box inside the Part container
- Start fillet or chamfer tool
- In the 3d view select an edge of the box
Looking at the call stack this is what happens:
DlgFilletEdges::onSelectionChanged reacts on the selection change and calls DlgFilletEdges::toggleCheckState. This calls Gui::Selection().addSelection() where object name is Box and sub-name e.g. Edge3.
Internally SelectionSingleton::checkSelection() fills up the passed reference of _SelObj and sets FeatName to "Part" and SubName to "Box.Edge3" and then it tries to find this entry in _SelList but cannot find it there because the passed pObjectName is still set to "Box".