[Milhouse]

The system I used before I got the RPi2 (and am using when I get tired of the RPi locking up) is currently running OpenELEC-Nvidia_Legacy.x86_64-5.95.1 and I don't have the problem. It has 4GB Ram and 1GB GPU Ram (I think).

Your x86 system almost certainly has the same ASS problem - I tested an OpenELEC x86-based system with ASS subtitles and observed the x86 system leaking RAM. It's just that your x86 system has well over 4x the amount of free RAM your RPi2 has, and it will take the x86 system a lot longer to exhaust all of the available RAM and show any problem..

These are very rough figures, but let's assume your 4GB x86 system has 3.5GB of free RAM, at a leak rate of 132KB/second it will take almost 8 hours of continuous playback before exhausting all available RAM. An RPi2 with about 700MB free RAM will take... 90 minutes.