Recently upgraded workstation to Server 2012 R2. Minor glitches with DF 6.0 Beta2. Most prominent is this one:
Most application windows cannot be minimized by clicking on the appropriate title-bar button when DF is running. A few, including Outlook 2013 and Chrome 33.0 can be minimized.
In all the cases where the minimize button no longer works, hovering over the button no longer selects it, or only for an instant> I have attached a short video demonstrating this.

I have no other windows mod software. I haven't tried reverting, as it has only been a minor problem. With multiple monitors, I can always move a windows out of the way if I can't minimize it. (Or turn DF off if I really need to) I had noticed the TitleBar button size as well. Font and scaling options are all default. I did have to add several right-side separators to avoid having the button in the middle of the minimize-maximize buttons.
Writing that last sentence made me think... I turned off the TitleBar buttons, and now minimizing works.

A couple of other odd thinks I've noticed:
When I start VMWare's VSphere 5.1 VSpere client, the logon dialog box opens in full screen, with the OK and Canacle buttons no longer visible. I can click OK or Esc, so it isn't a problem, but it's odd. I haven't seen another program do anything like that, yet.
If I set the Taskbar Transparency to anything other than 100%, and remove the check on Disable transparency, the Windows taskbar goes completely black, regardless of any settings I have made for it in Windows. To restore it I must check the Disable transparency box.
Also, the Send Metro app to window function does nothing at all. I've tried a few hotkeys, and a couple of apps. NJot something I care about, but I was curious.

Adjusting the horizontal offset seems to fix the minimize button issue, although the Move to Next Window icon is further corrupted, now showing up as an empty rectangle. (see screenshot)
The vSphere issue was a red herring - somewhere in the 2012 to R2 update process, several of my taskbar shortcuts were changed to Maximize. Fixed now.
I have the Desktop Experience installed. There are no themes I've seen for 2012 with transparency - nor do I care about it, I was just seeing what did or did not seem to work. Ditto for the Metro app - I have a couple I use, but putting them in a window is not important.
I am running server because I manage a network with almost 150 servers spread over 42 sites. Some of the tools I like to use seem to run better on Server than on Win8. My co-worker uses 8.1 on his system, and between the issues we both see, it's probably a toss-up over which OS is more convenient.

That does seem to fix the issue. When I first ran DF after upgrading to the Beta, the Taskbar icon was still a blank rectangle. Removing the horizontal offset setting and re-starting fixed that, and re-applying that setting, as a test, did not recreate the problem.