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I realized in the field that this female fly was sending "signals" - moving her legs like an ulidiid fly does...

Jindrich told to me: "Clusiids often have complicated behavior, both males (fighting for mating leks on trunks) and females (premating behaviour) which you have observed. Normally a male occupy lightened spot on a trunk (a lek) which he defends against other
males and waits for a female. When she visit the lek, both begin to visually communicate moving with fore (strikingly coloured) legs and wings. The larvae are xylosaprophagous living in rotting wood (in falled trunks or in stumps) of trees." I must try to testify this!!!