Surface active bum paper (6)
I believe the answer is:
appear
'surface' is the definition.
(I've seen this before)
'active bum paper' is the wordplay.
'active' becomes 'a' (grammatical abbreviation).
'bum' indicates anagramming the letters (bum can mean faulty or wrong).
'paper' anagrammed gives 'ppear'.
'a'+'ppear'='APPEAR'
(Other definitions for appear that I've seen before include "Become visible or seem" , "Become visable" , "Seem, look" , "Come into sight, materialise" , "Come on the market" .)