mouse and trackpad not functioning together

Hi, I recently bought the MagicTrackpad to work in conjunction with my Magic Mouse on the 27" 5K Retina iMac running Yosemite 10.10.2. The machine sees both devices and connects. However, when both are connected, the mouse stops working and as it moves around the screen, it selects areas which it highlights, a bit like if you were to select an area to cut and paste somewhere else. The Trackpad will move the mouse around the screen but none of the other functionality exists. If I turn the Trackpad off, the mouse returns to normal. If I turn the mouse off, the trackpad moves the cursor around the screen but has no other functionality.

I also have a Wacom Bamboo pad set up but this is not connected at the moment.

I'm very new to Mac machines, only getting this one in Dec 2014 so would appreciate any assistance anyone can give to help me solve this. Thanks in advance.