I am the developer who updated the plugin to 0.5.1. Thanks for reporting the issue. Unfortunately I have not been able to reproduce it thus far, which makes it hard to troubleshoot. Would you be able to provide me with the code you are using to register your custom meta boxes?
Also, have you tried disabling other plugins and reverting to the default Twenty Ten theme to make sure there wasn’t a conflict?
The more information you can provide me with, the better.