Hi,
Well I agree that you might expect to see the VBA project to disappear when you save it as vsdx, but on the otherhand, at that stage, even though the Save may have generated a (vsdx) file, you're still just dealing with the document in memory in your current session.
It's simply that the code can't be persisted in the vsdx format, so when you close the drawing and reopen it no code is available.
I think this adds up even if the dialogs suggest that the code is about to disappear.
Best regards
John