When saving a draft the file name is suggested, so far so good.
Untill ST7 MP1 the source file extention wasn't there, now it is. I hope this is a bug that will be solved in MP3?
I've been caught out by this as well. Not in ST7 (as we have not upgraded yet) but in ST6. Not a show-stopper, more of a minor irritation.
I can't remember this from the past.
For ST7 MP2: PR 8253794