Linux version 3.13.0-37-generic (buildd@kapok) (gcc version 4.8.2 (Ubuntu 4.8.2-19Ubuntu1) ) #64-Ubuntu SMP Mon Sep 22 21:28:38 UTC 2014)
AKA: Linux Mint 17.1, Rebecca, Cinnamon (64-bit)
The version you have installed is earlier than the release I am using, but the description of your problem is exactly one that I have been facing. The workaround described below works for me, and with a little bit of luck, may work on earlier releases...
I've been facing this issue too, yet have not found a fix for it, only a workaround.
I found that destroying (not closing) the application that has hold of the mouse operability, releases it's control over it. This is annoying when you're browser with 10+ tabs decides to lock the mouse...
The best work-around I found for it after some experimentation, is to use the 'Windows Special Key' to move the application in question around a little bit, and mouse /should/ be released. At least this has been working for me when it happens. Not ideal, but a quick alt-drag (my windows key is alt, you can set this in 'System Settings -> Windows -> Moving and Resizing Windows')
Best of luck!