Not all the time, but they're have been issues where the poor for of the lever has many that there was some pressure on the brake which blocked the small return hole on the piston which stops the fluid returning to the reservoir. The upshot of this is that when the fluid heats up it expands, it has nowhere to go other than push the pistons out, which adds more heat, which pushes the pistons out and so on, up to the point where one of two people have crashed with the front brake seizing on.
When I fitted them on an ER6 I had I made sure that, once fitted, that I could easily push the pistons back into the caliper.