why is this shape broken apart on subsequent opening of the file

This panel was built in DRAW using shapes:merge/subtract and left with a solid colour. On the subsequent opening of the file, it had become a piece of ‘art’… What should I have done to it before closing?
original drawingMonday morning piece of art?
(note: the ‘original’ image here is actually a ‘SPLIT’ of the one on the right with the bits moved back into their approximate positions.)

It is not clear how you have created the shape. If you were able to move parts, then you have likely not used ‘merge’ and ‘subtract’, but ‘combine’.
I cannot reproduce such behavior.

In general, when saving the file, nothing should be selected and you should have left point edit mode, otherwise you are not sure, that operations are really finished. And you might use in addition “Save a Copy”, open the so created file and compare it with the file you are working on. So you can detect save/open problems before you have finally closed the file.