In the selection tree, it's not possible to disselect two entrys at the same time. Whenever you disselect one of them, the other one becomes selected automatically and vice versa, although there shouldn't be any correlation.
I can reproduce this bug with the following two entries (in Situation - SituationRecord), but I think there are more faulty combinations like this):
1) Validity - OverallPeriod - validPeriod
2) GroupOfLocations - Location - NetworkLocation - destination
I confirm it seams to be a bug in the algoritm/rules that should make sure that we cannot select/produce an valid schema that always has the mandatory elements.
There was a bug when "parants" were requiered (gray).
Included in build 3902 released 2010-09-07