The solvent in the nitro block changes the properties of the liquid mask, and makes it difficult and unpredictable to peel off.
As mentioned, always re-cut around the edges to give it a nice clean seperation. You can always pull the masks off first then spray the nitro block but it gives the windows a 'frosted' look.
be carefull with it though as it can attack the water based paints.
Also, don't use it on chrome....it kills the mirrored look to it.
