This bug was originally marked as duplicate of bug 259161, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE Dev (Build 201706050001)
VM: Java HotSpot(TM) 64-Bit Server VM, 25.131-b11, Java(TM) SE Runtime Environment, 1.8.0_131-b11
OS: Linux

User Comments:
antoniocs: I was just copying code around and I got this error.
The code was this:
    struct Ball ball = {
        .coords.x = 120,
        .coords.y = 30,
        .coords.w = 20,
        .coords.h = 20,
        .left = 0,
        .up = 0
    };

GUEST: Ctrl + V

GUEST: Crash while re-do

GUEST: After the undo exception then tried to paste some text and got this issue

alied: after a previous exception tried to paste code in a JUnit test.

antoniocs: Another copy and paste error.
If  this happens again I will move back to the stable version




Stacktrace: 
java.lang.AssertionError
   at org.netbeans.editor.BaseTextUI.atomicLock(BaseTextUI.java:514)
   at org.netbeans.editor.BaseDocument$OldListenerAdapter.atomicLock(BaseDocument.java:1866)
   at org.netbeans.editor.BaseDocument.fireAtomicLock(BaseDocument.java:1924)
   at org.netbeans.editor.BaseDocument.atomicLockImpl(BaseDocument.java:1779)
   at org.netbeans.editor.GuardedDocument.runAtomicAsUser(GuardedDocument.java:354)
   at org.netbeans.editor.BaseKit$PasteAction.actionPerformed(BaseKit.java:2431)