Open to doubt (13)
'open to doubt' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for problematical that I've seen before include "Dubious" , "Open to doubt or debate" , "Presenting difficulties" , "Difficult; doubtful" .)
'open to doubt' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for questionable that I've seen before include "Open to doubt" , "Dubious" , "Controversial" , "Suspect, unproven" , "Doubtful - possibly dishonest" .)