(with Vavoom 1.26 (win32))
If there's a Boom linespecial 242 (fake ceil/floor, set sector's drawn height) the tagged sector's ceiling and floor are rendered according to the control sectors heights.
But if the tagged sector's ceiling is lower or if it's floor is higher than the control sector's ceiling and floor, and if the tagged sector sidedef's upper or lower textures are set something else than "-", Vavoom now draws those textures starting from the height of the tagged sector's ceil/floor heights.
In other words, the floor and ceiling are drawn correctly, but the upper/lower sidetextures are drawn starting from the wrong height.
A short demo wad: