Ah.That explains it (mostly). There are known compatibility issues with Spriter and some Wacom tablets/mice. We'll be trying to fix those issues in an upcoming free update build of Spriter. Sorry for the inconvenience. Cheers.
I know. I use a tablet with latest wacom drivers. may be its a bit different from normal mouse click. Its not a lot of trouble, because it does not happen continually, but it happens sometimes. If this happens to more people then may be its a bug, I know im not the only one ;)