hm i try again to explain… i never saw a feature to flip textures…
if you do not give a face any texture ,but the whole brush, then the back and the front (if they are parallel)
get the texture the same way:
if you now rotate the brush you see a 180° rotated texture =>flipped.
you only give the texture to the faces :
=> split your brush: every side needs to be splitted parallel to the side’s direction
e.g. if that is your brush (ignore the “*”, they are only here because " " arent displayed)
*//
/__/ then split it this way:__
*****************/// then you can give the whole " /" the texture, then rotate it 180°.
/_///
now surfaces on the top and at the bottom ´have the texture, too but they should have the texture
of the next side.
=> give those sides the other texture.
now merge the two pieces together: