Apologies if this has been mentioned before, I did a quick scan of topics and didn't see it.
I've modified the download directory many versions ago to E:\Downloads\$(GROUP)\. The sub-directories here have always had the full name of the group, e.g. alt.binaries.teevee. After upgrading to 6.40 build 2059 last night, and doing some downloads, the resulting downloads ended up in a directory called a.b.teevee. Took me a few seconds to work this out.
Not a bug, just a bit unexpected.