The gun seems to retain the power of the highest charged shot for all following shots.
Fire a level 1, nothing much as usual.
Fire off a level 8. KABOOM. Large explosion, drains the UPS a decent amount.
Then fire off a level 1 (or any other charge level) and it uses the same explosion as the Level 8 (but only uses the level 1, or whatever’s drain) instead of being a tiny little pebble of an energy shot as usual.
Tested the original UPS and it doesn’t have this bug.