I just fired up a client VM of 10.8.3 in Parallels on the Mac Pro & it runs OK there too. I'm assuming it's a server issue, but no idea what at this point. Only thing that immediately comes to mind is differences in network setups.

I've downloaded the latest compiled Deluge.app from the website from here: http://download.deluge-torrent.org/mac_osx/. I have a Macbook Pro (2012) & a Mac Pro (2008). Both are running 10.8.3, but the Macbook Pro is 10.8.3 client & the Mac Pro is 10.8.3 server. Deluge.app runs fine on the Ma...