Ah- I do see your logic. It wouldn’t have occurred to me, because I’m so used to how it does work. But yes- I totally grok how you’d have the expectation you did.
What it boils down to is- it largely just pulls in the template and treats it as if you were embedding a template from the current site. Which ... is actually how I expected it to work. Ditto the use of the channel tag- if it’s being pulled into ‘A’ it works just like it would if it was on an ‘A’ template- so you’d need to use the site parameter if you were pulling in site B content- even if it’s in a site B template and being embeded.
So- I’d say it’s expected and thus not a bug. But I can totally see how your expectations are reasonable. Given it’s a bit of a toss up IMO, I think for consistency it doesn’t make sense to make such a significant change.
Make sense? It’s working as designed, but how you thought it would work does make a lot of sense.