See below screenshots.
Grid is 1mm.
When red polygon is placed about 1.5mm away from green pad there is no generated clearance.
When red polygon is placed about 0.5mm away from green pad the clearance is generated and is 4mm as it should.
When doing a DRC check the polygon updates correctly though and it also updates correctly even if moved further away as in above statements, but I suppose you should not have to check DRC all the time in order for the polygons to have correct clearance.
