For me this seems to happen (quite often) with openjdk. With java from http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html it didn't happen (yet)
- Bug#837081: netbeans: Crashes due to assertion failure in ... Přemysl Vyhnal
- Bug#837081: netbeans: Crashes due to assertion failur... Markus Koschany
- Bug#837081: netbeans: Crashes due to assertion fa... Přemysl Vyhnal
- Bug#837081: netbeans: Crashes due to assertio... Markus Koschany
- Bug#837081: netbeans: Crashes due to asse... Přemysl Vyhnal
- Bug#837081: netbeans: Crashes due to... Markus Koschany
