To expand a bit on what Eugene has said, ID isn't really "saving" the open file as .idml when you use File > Save As and choose .idml as the type. It is exporting a copy of the file as .idml and no changes are made to the actual file you have open. The .idml format is really a compressed zip archive, and putting it under the save menu was a response to user pressure (used to be only under export), but it does not reflect the reality of what is happening.
↧