Boot Camp only detects two out of three monitors
From http://support.apple.com/en-us/HT204154


How many Apple Thunderbolt Displays can I use with a Mac in Windows 7 or 8 with Boot Camp?  
Most Mac computers can support one Thunderbolt display using Windows. The iMac (Retina 5K, 27-inch, Late 2014) and Mac mini (Late 2014) can support two, and the Mac Pro (Late 2013) can support up to six.