Since description page doesn't say that mesh should be 100% convex, thus I assume it is a bug.
Here are few meshes I experimented with:
Worst case. Doesn't show at all in editor.
For some reason I can't create new brushes after opening generated map.
Only part of original mesh exist in resulting map.
Fully convex. Works flawlessly.
Default conversion settings used.
Any additional info I can provide?