Magento stuck on product edit

[makrospex]

Since a few weeks when FPC is enabled on Magento 1.9.1.1 and editing a product in the admin area, the page keeps loading forever ("waiting for data from domain.com..." in the browser), on the second take. So editing the first product is no problem, but it hangs on the second one. It's a ngix server, using lsphp as php engine (php 5.6 latest) and you can see these processes are stuck in the shell via ssh. No server load, i guess it's just a broken pipe or something like that. request is processed on the server but no data is passed back to the client. When LestiFPC is disabled in Cache Management, no problem at all but results in a horrible time-to-first-byte (3-4 secs) in the frontend. The hoster said they didn't change anything on the system, apart from the usual updates (via "apt-get update" or the likes). No PHP Error, no server Error and nothing in the system.log, the lsphp child is just lurking around and takes no more requests until idle processes are cleaned up.

Admin pages aren't cached by FPC, are they? So it wouldn't make sense to exclude admin urls or blocks from LestiFPC, right? Any idea how to debug or solve this?

Thanks

[Quazz]

In what way does LestiFPC store its cache for you? Files? Redis?

[makrospex]

Sorry, forgot that. LestiFPC stores Files. There is no problem creating and writing to the cache directories.