Close button sends client to the tray, statically linked Qt for OSX.
See the Changelog for list of features and fixes currently only available in the nightly builds.
I would like to ask if there is any specific reason for not having current builds for Linux? Is it the lack of interest or is it some technical difficulty? I would like to use the Linux version, but it crashes and I believe(/hope) it's one of the bugs that you've fixed recently (the floating point/division by zero issue with the MP3 scanning code), so I'd like to give it a try before digging deeper into the problem.
Let me know if I can be of any help.