Very strange history behavior after FUSE

Hi people! I'm FUSE-ing two simple shapes (boxes). After that I ask BRepAlgoAPI_Fuse for history and get very strange results: the first solid body (BODY1) is removed, and at the same time, one of its face are modified. What the hell? Why BODY1 was removed?

I expected completely different results: i assumed that nothing would be deleted and that one of the faces of the first solid (BODY1) would simply be modified (the face that merges with the second solid). Why am I getting different results?

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