[Lingo] 話だが

[steve smith <sjs@example.com>]

Can someone shed some light on '話だが'?

The original sentence is from a translation of Holes.  It reads:
夏のあいだ、昼間の気温は、日陰でも摂氏三十五度前後ーー日陰があればの話だが。
and means "During a summer day, it's 35 degrees C in the shade -- if you 
can find shade."
Literally I think it means "to say but" and is used in phrases like ここ 
だけの話だが (between us) and 奇妙は話だが・妙な話だが (strange to say) 
and from a web search, it seems to be fairly common, but I can't get a 
feel for how to use it.
Thanks
Steve S.