I have been randomly reading the GH2 source code recently, and I found some small bugs. I will collect what I find here, as the Sourceforge bug tracker doesn't seem to be used.
(effects.pp lines 2931 and 2954) Charge attacks use the Ranged Combat skill (#4) instead of the appropriate mecha skill, and it doesn't use any stat. (fixed in SVN)- (gearutil.pp lines 2369 and 2372) For every 5 points of DC, RollDamage roll between 0 and 9 for damage, for an average of 4.5 instead of 5 (may be intentional).
(action.pp line 602) BRUTAL weapons have reduced efficiency against Anti-Beam armor, while the comments indicate that HYPER weapons should be the ones affected. (fixed in SVN)