Ah, well at the moment I have 3 rotation angles around the x, y and z angles. The block of code above translates the rotation angles into a 3x3 rotation matrix. Everything works as expected, except when rolling on the Z axis (roll).
If I start the app when I'm at the default orientation, then perform a Z axis rotation, it works fine, however if I rotate 90 degrees around the Y axis first (yaw) and then perform the Z axis rotation it appears to perform the Z axis rotation as if the Y axis rotation hadn't taken place. So after rotating 90 degrees around the Y axis and then performing a Z axis rotation, the camera seems to forward roll.
So basically, any Z axis rotation ignores any other rotation (around X and Y) and just rotates as if it was rotated around the original orientation.
Sorry if that's a bit long-winded.
Just trying to be descriptive.