Acts not allowed, as it happens (5,3)
I believe the answer is:
turns out
'as it happens' is the definition.
(I've seen this before)
'acts not allowed' is the wordplay.
'acts' becomes 'turns' (turn is a kind of act**).
'not allowed' becomes 'out' (I've seen this before).
'turns'+'out'='TURNS OUT'
(Other definitions for turns out that I've seen before include "as it happens" , "Empties" , "Gives order of the boot" .)