I've never seen this before, but there is a first time for everything, eh?
Are you creating a softkey template from scratch or copying one that already exists and editing it? (Or have you tried both already?)
What exact version of CUCM are you running? (Not just "11.5" but "11.5.1.10000-6")
And, yes, this is probably some weird bug and it may take TAC to fix it.
Maren