Acting oddly, one's hidden the label (2,5)

I believe the answer is:

on stage

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'acting' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for on stage that I've seen before include "in front of a audience" , "performance" , "Treading the boards" , "in a play?" , "like passengers in Wild West" .)

I've seen this clue in the Evening Standard.

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