I absolutely agree with this. I've been caught out by it several times now. (Designer v188.8.131.52)
The worst part is when you come to close the document. It doesn't close as expected, instead you are presented with the option to SAVE. This is unexpected, because you've been saving all along, so the instinct is to hit CANCEL. But cancel doesn't go back to where you were, with the document open, instead the unsaved document is CLOSED! And your work is lost.
I'm sure this is quite an obscure scenario that QA haven't got in their tests. But it absolutely needs to be caught. Either ctrl+s should warn if a save doesn't happen (why wouldn't anyone want that from an application?) or the cancel button at the end shouldn't close the document. Ideally both of these.
Apart from this, I'm still enjoying Designer and Photo as my Adobe replacements. Keep up the good work.