I have tons of xp and never seen a leak without those. Experience is ive written over 8k lines in #FTB helping people.It's not exactly from those mods. It's an error in mojangs world code. However, the leak only ends up becoming a problem when a mod accesses a certain hook into that section of the code.
If your not running those particular mods, the code doesn't execute improperly (the error still shows up if you are testing in Eclipse,) but hangs the world if you are.