I second that , i have seen that too (just on some fresh radio mission (council/crey) , mission lvl 36 set to -1 ) and all enemies are Lvl 36 instead of 35 as they should be and i consider it a Major Bug for soloing not perfect chars unless Devs dont want -1 anymore but then it should be completely removed.
Probably the no more +1 in some rooms of Mission change did have this unwanted side effect so instead of +0 in some rooms, i have em now in ALL Rooms, bad change if it was intended if u ask me.