Each and every heavy duty, high-end mouse experiences this problem after about a year or so.

Your most valued customers are left disappointed with mice that look like they are working properly, when in fact they are not. This is a well-known problem, but it doesn't concern users that are using their mice just to perform ordinary clicking. On the other hand, users that do a lot of dragging and need to perform long, holding clicks are plagued by this.

The problem is that Omron's micro switches develop a layer of corrosion or dirt on the very tip of the contact spring, which makes electrical contact flaky and non consistent, resulting in unwanted double-clicks and unwanted dragging drop offs.

The problem could be fixed by better insulating contact plates from the outside atmosphere or using some other material that would provide a more stable long term contact quality.

This problem most probably exists on all mice, but is most prominent on high end mice that power users are using for various power tasks and gaming, like Logitech, Razer and similar.

http://zalbee.intricus.net/2014/02/how-i-fixed-my-logitech-g500-mouse