Yes, I understand the system. The mojo bar fully charged from 40 to 41, then dropped back to the bottom of 40. I already got the reward for level 40 by the by.
(Sorry for the report, I replied to the wrong place)
I did level 41 three times, and it sends me backto 40, without giving reward. It did this on earlier levels as well, but I wasn't sure because then it only did once, but now I paid particular attention to it