Could you check the error log of Sitefinity to see if it contains any relevant information - App_Data/sitefinity.log.
If you are running behind any proxy the submit could be performed 4 times. There is no such bug in the module. Service unavailable is a server side error and possible reason could be if you have made any modifications of the module/views that could cause an endless loop which kills the server.
All the best,
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items