java.lang.IllegalStateException: Trying to remove a cached item that's not in the cache

I have seen this exception twice today so far. What's very worrisome is that it is intermittent and happens for no apparent reason.

I have not been ale to reproduce it when I tried, but the one common characteristics when it happen both times was that I just run my app, then waited for about a minute, then pressed RIGHT arrow key.

I'm attaching the sample app and the log that is an input file.

To reproduce the issue on Mac you need to put the "log.txt" file in ~/Desktop, so that it will get automatically read at the app's startup. The NetBeans project for the app and the log.txt are attached.