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Well, that was exactly why I didn't want to suggest a name. You would all rush to the relevant couplet in the key and then work your way backwards ;) Like I do alot!
Okay, here goes... This should be Paratrixa polonica, female.
I first keyed it in Tschorsnig & Herting and didn't really believe it. Then I tried the key in the Manual of Palaearctic Diptera and arrived at the same species. I could of course have made the same mistakes twice, but the approach to this genus differs a bit in the two keys, so I'm pretty confident that I'm right.
If so this is indeed a rare find and well outside the range of the species given in Tschorsnig & Herting.
But have a look at it now :)