trackpad zoom locking in games

My trackpad pinch-to-zoom works fine in Safari and other applications.

It is not working properly in the games I've tried on steam (Europa Universalis 4 and Crusader Kings 2) and in apps downloaded from the App Store (Hearts of Iron III). I pinch-to-zoom into the map and nothing happens. After a few attempts sometimes it does zoom in once, and then gets stuck. I cannot zoom out again or zoom in further, no matter how many times I try.

I have updated to Yosemite and installed all the updates from the App Store. The games mentioned have the latest patches installed and steam is also up-to-date.

I've not played games in a while - a few months ago when I last played everything was working fine.

In Settings/Trackpad pinch-to-zoom is activated. In Settings/Security&Privacy, under Accessibility, steam is allowed to control my Mac. I've tried turning these settings off, re-booting and then turning them back on. This doesn't work.

Apart from pinch-to-zoom freezing everything else works normally e.g. I can scroll and click in games using the trackpad.

Any suggestions?

Thanks v much.