BBC world are hinting that the Turks shot down the bomber because it was, or rather its squadron mates have recently been attacking the "Turkmen", an armed group active against Syria's leader and Govt. but close to Turkey in every way kith and kin like.
Looks like a mistake, really.
I've left Max Hasting's recentish excellent book about the crazy start to WW1 at home, but this is ringing warning bells right in my head. The imbecile nature of the European leaders, I mean, at that time.