Shiny Server JavaScript error: Can't remove headers after they are sent

I'm using the open source server and have started receiving the following javascript error:

"Can't remove headers after they are sent".

Unfortunately, the log is not very informative. It identifies a javascript error, but not the generating app. I presume there's a problem in the autogenerated javascript, but I'm not at all clear on how to go about debugging. Any pointers or suggestions appreciated.