I fell to my death digging out the pool and when I respawned I was floating in space for a while with no terrain at all, then it booted me out and I can't reconnect now :(
A browser's default behaviour should be treating it as an executable, because people that know/care they are zip files (the minority) will know how to override that behaviour, whilst people that don't will get all confused.
Well, if there's different content types to specify that, then yeah.
(And, if it hasn't explicitly been set by the uploader, the default behaviour should again be to determine if its an executable JAR and act accordingly.)
my browser (IE8) did detect it and act accordingly - maybe spinningplates has buggered about with some settings or installed some software that hijacked the .jar extension?