If anyone was curious to know, or if perhaps you didn't notice... Locking buffs on an NPC (common with things like Embrava, brew, etc.) does not work for maneuvers.
Display wise, your buffs show that you still have the maneuver. However, the maneuver only works for 1 minute regardless.
Tested this locking my dark maneuvers on a casket and looking at refresh on my spiritreaver. With three maneuvers on, and not full MP, I had refresh of one maneuver at first, and then no refresh with three dark maneuvers on. The maneuvers eventually wore off.
Essentially, it's not a big deal but locking maneuvers does nothing but display them graphically.
Not sure if this is common knowledge or not, but just felt like sharing.