Pixmap practical size limitation?

["Jerry Miller" <gmiller at cs dot sunysb dot edu>]

In modifying an existing application, which contained
one (scrolled) DrawingArea and two (scrolled) Text
widgets, I wanted to use multicolor text and decided
to use two more DrawingArea widgets to accomplish
this.  However, only the 2000x2000 original Pixmap
is reliably written for the refreshment of the original
DrawingArea.

In order to accommodate the potentially long and/or
wide range of text in the emulated Text widgets, I
created a Pixmap of size 5000x4000 and 10000x2000,
respectively.  To be sure it wasn't something in the
rendition of the text strings that was at fault in their
unpredictable behavior, I drew a black 20x100
rectangle in the upper left corner of each Pixmap
immediately after creation.  Only the one for the
2000x2000 Pixmap appears in the associated
DrawingArea window.

Other than their sizes (and the variable names,
of course), there is virtually no difference between
these Pixmaps.  In fact, if I temporarily change
the dimensions of the other two to 2000x2000,
I find that their behavior becomes reliable once
again.

None of the X documentation mentions any
size limitations for the Pixmap, whose datatype
is "opaque."  (Thanks a lot, MIT!)  Even if
there were one, it should generate a predictable
error message, rather than an unpredictable
behavior.  Anyway, even if "unsigned int"
referred to 16 bits on my computer (which it
does not), these dimensions would still be
within range - for that matter, they would even
be accommodated by "signed short"!

Is this a known bug?  If so, can I get around it,
albeit kludgily, by declaring 21 variables of type
Pixmap and doing redundant XDrawString()
calls to be sure that any that might fall withing
the bounds of the write will be updated, or is
there a limit on the _total_ amount of memory
available for Pixmap data?

I am running under Windows NT4, SP3, with
the Hummingbird Window Manager, v.6.1.
(The window manager supplied with cygwin
is impractical for any sophisticated applications.)