Why are you so concerned about this? You started the thread asking if anyone knew of accidents during pushback with parking brake set.
I assume you don't know of any, nor the pprune community by the look of it. Certainly Google doesn't.
So it would appear the risk is relatively low, as long as people stick to standard calls and sop.
Perhaps the towbar is designed to give before the gear assembly.
Perhaps you worrying too much about it.