I am using Visual SourceSafe as VCS
And there is wrong behaviour (correct me if i wrong) of IDEA.
I make checkout file and editing it. Then i try to checkin. If i checkining with standart VSS client then IDEA shows that this file modified (name of file clolored with green), but if i checking with idea (contex menu->source safe ->checkin) then everithing all right (header is black).
Seems that IDEA and MS client process blank space in different ways.