Multirest in second ending

I understand how Multirest works - and mostly it works fine. I've got a nice score going... but in the parts there is a slight problem When I have a second ending of one bar of rest and the next bar following is also a bar of rest, they don't seem to combine as a multi-rest. I think the volta for the second ending is telling Multirest that the bar is not empty. (Just in case, I've selected each bar individually and pressed "delete" - no change.) I've also tried selecting both bars and pressed "M" - but that didn't do anything (I don't think it's supposed to work that way, but, heck, I'm stumped! I'll try anything!)
If this is expected behavior - any one have a work around?
Take a look at measure 21 and 22 in any of the trumpet parts.