End of contribution strange — editor made a mistake? (6)
I believe the answer is:
nodded
'made a mistake?' is the definition.
(I've seen this before)
'end of contribution strange editor' is the wordplay.
'end of' suggests the final letters.
'strange' becomes 'odd' (I've seen this before).
'editor' becomes 'ed' (abbreviation).
The last letter of 'contribution' is 'n'.
'n'+'odd'+'ed'='NODDED'
(Other definitions for nodded that I've seen before include "Let the head drop" , "Made head movement by way of assent" , "Bent the head in sleepiness" , "Indicated assent or recognition" , "Signified agreement" .)