Maybe there are not standard bolt head/nut dimensions defined in UTS so these were not implemented as fixed values? But maybe it should be that the selection of thread type and size just sets the expected thread values but does not prevent the user from modifying them.
I also noticed something else is strange - If you create a hole without thread profile selected, exit hole creation - all Ok. Enter hole edit, select thread profile, exit edit - Ok. Enter edit, set profile to none - error "Thread size out of range" when trying to accept the changes.