[MC-23105] Exception in Server when exiting

When exiting a freshly created minecraft Server with Ctrl+C on the linux console, I got a lot of console spam. The messages all were

java.util.ConcurrentModificationException
        at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1115)
        at java.util.TreeMap$KeyIterator.next(TreeMap.java:1169)
        at jr.a(SourceFile:454)
        at aed.a(SourceFile:217)
        at aed.a(SourceFile:91)
        at jq.b(SourceFile:154)
        at jq.a(SourceFile:183)
        at jr.a(SourceFile:602)
        at net.minecraft.server.MinecraftServer.a(SourceFile:263)
        at net.minecraft.server.MinecraftServer.m(SourceFile:283)
        at hg.run(SourceFile:566)

Being able to code a little bit in Java, this seems to be a severe bug (race condition or missing synchronization or something).

After restarting the server some chunks looked as if they were not saved correctly.

This is reproducible.

Can attach additional files like server.properties if necessary.