The LayerMask control gets confused if there's any of these special characters in any of the layer names: & % ^ # _ and any non-ASCII characters. The reason is that the function CompareMenuItemName (MenuController.cpp) calls GetMenuNameWithoutHotkey on the layer name strings which strips part of the layer name away. To fix this issue we need better control in MenuController of whether a menu should try to strip hotkeys away or not.

Edit: There needs to be layer with the name Foo and Foo_Something for this to break. Foo_Bar and Foo_Bar2 would work fine together.