Download attached example application and perform following:
1. Run it on JDK1.3.1 and on JDK1.4 (concurrently)
2. Try to copy/paste from/to app on JDK1.3.1 to native editor, it works OK (use Ctrl-C and Ctrl-V)
3. Try to copy/paste from/to app on JDK1.4 to native editor, it works OK (use Ctrl-C and Ctrl-V)
4. Try to copy/paste from app on JDK1.3.1 to app on JDK1.4, it does NOT work (use Ctrl-C and Ctrl-V)
5. Try to copy/paste from app on JDK1.4 to app on JDK1.3.1, it works OK (use Ctrl-C and Ctrl-V)

So, the problem is copying from JDK1.3.1 to JDK1.4, which does not work.

Used JDK:
JDK1.3.1:
java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Java HotSpot(TM) Client VM (build 1.3.1-b24, mixed mode)
JDK1.4:
java version "1.4.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta2-b77)
Java HotSpot(TM) Client VM (build 1.4.0-beta2-b77, mixed mode)

This was originaly issue:
http://www.netbeans.org/issues/show_bug.cgi?id=14923