Stew: tiny bit unfinished -- that's a problem (3,6)
I believe the answer is:
hot potato
'that's a problem' is the definition.
(I have seen 'Tricky problem ' mean 'hot potato' so perhaps 'problem' could also mean 'hot potato')
'stew tiny bit unfinished' is the wordplay.
'stew' becomes 'hotpot' (I've seen this before).
'tiny bit' becomes 'atom' (I've seen this before).
'unfinished' means to remove the last letter.
'atom' with its last letter taken away is 'ato'.
'hotpot'+'ato'='HOT POTATO'
(Other definitions for hot potato that I've seen before include "Difficult issue" , "often being seen in a jacket" , "Difficult matter" , "Troublesome thing (in a jacket?)" , "Hard-to-handle situation, like fiery spud" .)