It was discovered that with OtherDrops installed, McMMO's Treefeller doesn't always seem to work. I have tested this myself and can personally confirm that atleast on smaller trees, they don't always "pop". I have reports that larger tress still break apart with mcMMO's treefeller however, and I have left config to it's default except for the range setting.

OtherDrops 2.8b.573
CraftBukkit 1.7.9 (no idea build number)