There's a similar trick with vulnerable (minus 5 spell resistance) and brilliant (+1 intelligence per level).  Intelligence increases spell resistance in addition to helping spell mastery and making you get XP faster.  Hopefully by the time anyone is throwing dangerous spells at you you have enough levels so resistance is a wash and the mastery & XP bonuses are free.

Worked really well in .78, might not be quite so good in .86 now that champs level slower if you keep them together.

Would just like to point out that this little nonsensical bit of balance is still present as of Beta 4, possibly somewhat worse as now Natural Leader is"free recruiting", making the pair more appealing.

Yep these do not cancel out. You are usually better off taking the hit allies one and just manuevering so you dont hit allies.