Pretentious attitude over publication is a minor matter (4,5)
I believe the answer is:
side issue
'a minor matter' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'pretentious attitude over publication' is the wordplay.
'pretentious attitude' becomes 'side' (I've seen this before).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'publication' becomes 'issue' (synonyms).
'side'+'issue'='SIDE-ISSUE'
'is' is the link.
Can you help me to learn more?
(Other definitions for side issue that I've seen before include "Adjunct" , "That's not so important" , "It's not an important matter" , "Illegitimate children" , "Incidental minor matter" .)