Short answer, I don't remember.
Long answer, While working on a routine the did something to a viewport there was a need
to select the viewport & someone testing discovered it would not select an irregular vp.
So the search was on & I found or was given the answer. 340 !
If I found it it was at AutoDesk forum or if someone suggested it I don't remember who.
I found an old link to a previous post but the link was lost during the transition to
the new board. Sorry.