Shift-Caps Lock-Tab not working with remapped Caps Lock

I've remapped my Caps Lock key to Ctrl using the Preferences > Keyboard > Modifier keys dialog and in the following question when I say CTRL i mean the Caps Lock key remapped to Ctrl and Ctrl is the normal left Ctrl key.

I'm using OS X 10.9.4 and I've just bought 2 new external corded Apple keyboards and both of them are having trouble with the key combination Left Shift + CTRL + Tab. For applications where that combination should go to the previous TAB it does not work. If I use the right Shift instead it works fine, if I use the left Ctrl key instead of the remapped Caps Lock key it works great too.

The internal keyboard on the laptop works fine with Left Shift - Caps Lock - Tab.

The computers are a Macbook Air 11" Mid 2011 and a Macbook Pro 15" Mid 2010.