when a masked PImage is drawn before (draw order) and in front of (translate z) another object, the PImage's matte is drawn opaque over the other object.

Code:

import processing.opengl.*;

PImage img, imgAlpha;

void setup () {
  size (400, 400, OPENGL);
  
  img = loadImage("image0.gif");
  imgAlpha = loadImage("alpha0.gif");
  img.mask(imgAlpha);
  
  stroke(250);
  fill(150);
}

void draw () {
  background(0, 0, 50);
  
  pushMatrix();
    translate(0, 0, 0);
    image(img, 50, 50, 200, 200);
  popMatrix();
  
  //if rect is drawn after (draw() order) and behind (z depth) alpha masked image,
  //alpha mask works incorrectly
  pushMatrix();
    translate(0, 0, -1);
    rect(150, 150, 200, 200);
  popMatrix();
}
 

workaround is to either draw masked PImage after or behind other objects.

example images:
http://transmote.com/share/p5/alpha0.gif
http://transmote.com/share/p5/image0.gif

this is with winXP, v0087.

now tracking this issue here:
http://dev.processing.org/bugs/show_bug.cgi?id=176