Thanks for your examples : it really help to fix the issue.
Unfortunately, there seems to be an issue within GraphViz. We've been able to build a beta that turns around this issue in some cases. Your examples are working fine with it, but other may probably fail. Do not hesitate to post again when you'll have some other crashes.
Here is the beta https://dl.dropboxusercontent.com/u/13064071/plantuml.jar