Acting a bit insane while away (2,8)

I believe the answer is:

in absentia

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'while away' is the definition.
(I've seen this in another clue)

'acting a bit insane' is the wordplay.
'a bit insane' can be anagrammed to 'IN ABSENTIA'.
Though, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for in absentia that I've seen before include "away" , "Wanting an appearance" , "While not present (Latin)" , "not at event" .)

I've seen this clue in The Irish Times and the Irish Times (Crosaire).

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