Yes I think it is. I reported something similar a few weeks ago.
Try this code:

int x;
int y;
void setup() {
 size(400,400, P3D);  // DELETE P3D and it works fine !!!
}

void draw() {
 background(122);
 x = mouseX - 20;
 y = mouseY - 20;
 rect(x-10, y - 5, 4, 10);
 rect(x, y+10, 4, 12);
 rect(x+5, y-10, 12, 4);  
}

You see how the rects are drawn in different sizes when you move the mouse?

Basically the P3D renderer is drunk or on drugs, it does nothing straight.

Your code works beautifully in the OPENGL renderer.
(which still is quite buggy as well, but hey, it will get there)...