Can only boot Windows when selected at boot time

If select Windows at boot time (holding ALT/OPTION), it boots fine.

If I select Windows via Boot Champ (OSX), Startup Disk (OSX), or Boot Camp Utility (Windows), on next reboot or powerup the fullscreen whitish/greyish screen never goes away and nothing boots up.

I have Yosemite on an SSD in bay 1 and Windows 8.1 EFI on a separate SSD in bay 2. Computer is a 2010 Mac Pro.

I switch OSes a lot and it's a hassle to sit and wait, and time the keyboard press, wait longer for the OS options to appear, etc. Obviously I would love it if I could get the usual boot switching methods to boot Windows.

I've tried clearing NVRAM multiple times. Anyone have any thoughts or helpful tips?

 

Bump...

...any thoughts? I don't even know where to begin to troubleshoot this.