Alan, it looks like FTM 2012 has a problem with that filter. I have a tree that I have a copy in FTM2012 and a copy in FTM Mac 2. When I filter by blank death date in FTM2012, I get 10 records - all ten have a Death fact with a place or description, but no date (just like you're seeing). In FTM Mac 2, I get 923 records - the same ten, plus 913 others that don't have a death fact. This is a bug.
I will report the bug to firstname.lastname@example.org
& suggest you do the same.