Brush order broken (?)


I was just prototyping a level and discovered that the brush order does not seem to work properly.
I never noticed that error before. Im currently using 4.6 (the official release).
I placed a subtractive brush in the level which raised the ceiling of a room. Consequently I had to make the pillars higher.
However I tried, (make the pillars last, make the subtractive brush first). The pillars would not get rendered beyond the initial ceiling height.
Copying the brush solved it.
Do you guys have similar expieriences?