RW 6.3.7 File Size - Whats Going on Here?

I noticed when I right clicked and duplicated a project file I’m working on that the duplicate was Over 10 times as large.
Thinking this was strange, I did a save as from Rapid Weaver and got the same result.
I did a few more edits, saved the original and then did a save and a save as and a duplicate … same thing again.
I do this all the time while working on projects and have never seen this before.
Screen shot attached
Anybody know whats going on here?

RW 6.3.7 (15153)
Stacks 3.1.0
Foundation 1.7.2
Foundation stacks 1.7.7
Easy CMS 1.1.2

EDIT: I did the usual restart Rapid Weaver, restart Mac.