This regression may be introduced in the fix of the following bug:
http://monaco.sfbay.sun.com/detail.jsf?cr=6944561
This regression happened on the following two machines:
Solaris 5.10 (SunOS awt-sqe7 5.10 Generic i86pc i386 i86pc)
Gnu Linux (Linux d2-comet 2.6.22-14-generic #1 SMP Tue Feb 12 07:42:25 UTC 2008 i686 GNU/Linux)

To verify it, please compile and run TestCursor.java in the attachments for CR 6944561.

Here are the details:
on the machine: SunOS awt-sqe7 5.10 Generic i86pc i386 i86pc

/net/jarchive.sfbay/export/jcg/NB.archived/6u23/client/2010-09-15.6u23/solaris-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
run fine.

but
/net/jarchive.sfbay/export/jcg/NB.archived/6u23/client/2010-09-20.6u23/solaris-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
gave the following error:
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 20 (X_GetProperty)
  Resource id in failed request: 0x0
  Serial number of failed request: 188
  Current serial number in output stream: 188

and
/net/jarchive.sfbay/export/jcg/NB.archived/6u23/client/current.6u23/solaris-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
gave the same error:
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 20 (X_GetProperty)
  Resource id in failed request: 0x0
  Serial number of failed request: 188
  Current serial number in output stream: 188

For XToolkit, it run fine.
/net/jarchive.sfbay/export/jcg/NB.archived/6u23/client/2010-09-20.6u23/solaris-i586/bin/java -Dawt.toolkit=sun.awt.X11.XToolkit TestCursor
run fine


on the machine:
Linux d2-comet 2.6.22-14-generic #1 SMP Tue Feb 12 07:42:25 UTC 2008 i686 GNU/Linux

/net/jano1.sfbay/export1/jcg/ws-depot/6u23/client/nb/archived/2010-09-15.6u23/linux-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
run fine

but
/net/jano1.sfbay/export1/jcg/ws-depot/6u23/client/nb/archived/2010-09-20.6u23/linux-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
gave the following error:
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 20 (X_GetProperty)
  Resource id in failed request: 0x0
  Serial number of failed request: 218
  Current serial number in output stream: 218
and
/net/jano1.sfbay/export1/jcg/ws-depot/6u23/client/nb/archived/current.6u23/linux-i586/bin/java -Dawt.toolkit=sun.awt.motif.MToolkit TestCursor
gave the following error:
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 20 (X_GetProperty)
  Resource id in failed request: 0x0
  Serial number of failed request: 217
  Current serial number in output stream: 217