I'm sure there are a lot of bugs.

Let's cite the most critical :

* When you plot an isosurface (in 3d) on a deformed configuration,
if you change the exageration factor, the iso may fall outside
the outline of the domain.

* When you save a bitmap image (or a sequence of images to make a
movie), it may happen that the result is uncomplete when the xd3d 
window is obscured by another window during the saving process.
In this case, do it again being sure that nobody is hidding any part
of the displayed image.

* The popup windows appear over the main window. If you try to move
the popup, the obscured part of the main window may become black 
until the popup is destroyed. It happens for example on linux/XFree.
The cause is known (no backing store on the X server) but it is not
so easy to fix it.

* In the same spirit, it may happen that the main window is not
properly refreshed for various reasons. In this case, resize a little
bit the window (1 pixel is enough) and it will be redrawn.

* In some cases, in 3d, when the elements are very elongated,
the hidden faces algorithm, which is quick but not perfect, can
show artifacts (a portion of face behind displayed in front of
another one).