@jschauma Interesting.

I hadn't realized Outlook does this either, and now this has led me down a rathole. If this is just surprising, but technically acceptable I'm unsure. Few references I've found so far make it any clearer.

Maybe this is just yet another example where implementations can come to reasonably different conclusions on how to handle some ambiguity in specs? Microsoft does seem to have come to a different interpretation than all others I've tested, that would suggest something.