all it does is double your chance to upgrade TH, Not give you 100% upgrade rate.

Example: You have 10% Chance to Upgrade TH, With Feint on, You have 20% Chance. Willing to bet this is not a glitch, Its just working exactly as i said it would work.

(Edit: But thanks for reporting it, If it is a glitch, I'll be happy :O, but I'm expecting this to be it )