Running 1.8 with Catalyst 14.7 the issue seems to be fixed.
Since reporting this I have updated to Java 1.7.0_65 from 1.7.0_51, which seems to have fixed the issue across all versions.
Versions 14w30b & 14w30c appear to have fixed the issue, at least for me.
I can confirm closing Overwolf has fixed the issues for me.