If VIEWMOL runs in color map (that should only happen on IBM RS6000 with Sabine graphics adapters if anybody still has one of these, in this case the background of the title screen has a constant color instead of the usual dark top and lighter bottom) shadows are not drawn if the drawing mode is ``with surface".
On some graphics boards VIEWMOL will not be able to get a stencil buffer (notably Intel graphics chips). VIEWMOL will silently continue without the stencil buffer, but this will result in artefacts in the shadows drawn.
If TIFF or PNG files are saved make sure no other window (including dialog boxes) overlaps with the window to be saved. The information is read from the screen and overlapping windows might show up in the saved file (this is hardware dependent).
HPGL outputs for drawings which are labeled with non-latin characters will not contain any labels. HPGL output has only support for German umlauts, Postscript provides all ISO-8859-1 and KOI-8 characters.
If VIEWMOL runs on FreeBSD there are problems with saving molecules in any format. The output filters never return and therefore VIEWMOL seems to hang. Pressing Ctrl-C in the terminal VIEWMOL was started from terminates the output filter and makes VIEWMOL work again, but no meaningful information is put into the output file. A work-around for this problem is currently not known.
VIEWMOL is usable with Lesstif (> 0.81). There are, however, some glitches, e. g. shortcuts don't work.