Cleansing corrupted area removes "+1 To Monster Level Area" on Maps

I recently cleansed some of corrupted areas where there was at least one Map with +1 modifier. After cleansing this modifier is gone on each of these Maps.

I know, starting from 0.2 only few Maps (observed max 2) in a corrupted area had a "+1 To Monster Level Area" modifier.

Cleansing the area left the +1 modifier so you could still go +2 together with Irradated. Now the +1 gets deleted after cleansing. This is even worse than introducing "+1 To Monster Level Area" on just a few corrupted maps.