X forwarding and BadWindow error

[Andreas]

Has anybody else experienced weird X11 forwarding problems such
as the one below:

andreas at teste10:~> x3270
X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  3 (X_GetWindowAttributes)
  Resource id in failed request:  0x404372
  Serial number of failed request:  833
  Current serial number in output stream:  834

or

andreas at teste10:~> gq
Gdk-ERROR **: BadWindow (invalid Window parameter)
  serial 737 error_code 3 request_code 38 minor_code 0
Gdk-ERROR **: BadAccess (attempt to access private resource denied)
  serial 738 error_code 10 request_code 102 minor_code 0

The application opens, but crashes with this error when I open a menu.

Without ssh (that is, using export DISPLAY=mymachine:0), it works.

My XFree86 version is 4.4.0, and openssh is 3.8p1.
Trying from older XFree86 and openssh, it works. I couldn't isolate
it yet, whether the problem is with X or openssh (or something else).