This bug didn't happen in 2.1 (first gif), however, 2.2 changed the Linedef type 7 setup, and it seems that the changes to the linedef made the effect not work propely anymore on Polyobject flats (second gif).
I also uploaded the maps I made for comparison, for each SRB2 version.
Version 2.1.15:
View attachment srb20868.gif
Version 2.2.6:
View attachment srb20837.gif
I also uploaded the maps I made for comparison, for each SRB2 version.
Version 2.1.15:
View attachment srb20868.gif
Version 2.2.6:
View attachment srb20837.gif