It just ends up that way sometimes. I write mostly in plain text, or in a programming language. Sometimes smart-paste will add a space, while plain-paste won't. So sometimes I do "space cmd-V", others "cmd-V" space", or "space cmd-V" space". And sometimes I just fat-thumb the spacebar.4? Dude where?
As I said, I don't worry about it much. When I do care, search-and-replace is ready and waiting. And if I bungle search-and-replace, undo is ready for that.