I had the same issue with the PVR Clients and have managed to resolve it, but it took a bit of fiddling around.
Recently there has been a bump of the minimum API version required for the PVR clients so you should see this line appear in the XBMC log file:
ERROR: PVR - Add-on 'Tvheadend HTSP Client' is using an incompatible API version. XBMC minimum API version = '1.9.1', add-on API version '1.9.0'
Putty into the PI and type the following to check: (it will be near the start of the log as its initialised when XBMC/Kodi first starts up)
I can't remember where I read it somewhere, but the PVR Clients are not updated as part of the nightlies and only seem to be updated properly when RaspBMC is installed. It is however possible to get the latest pvr client source and compile them yourself - which is what i ended up doing. (Unfortunately I couldn't find any precompiled for use - not sure if it would work, but I could upload the zip for mythTV that I generated/compiled)
The Git Repo where the source is can be accessed here: https://github.com/opdenkamp/xbmc-pvr-addons
and the readme gives a guide on how to do the compiling. (On a PI it may take a little while)
If you compile them into zip files and then just install the addon from that zip, that worked for me. (Although i did delete all of the PVR Clients addons before i did this)
The source was updated about a month ago increasing the version number from 1.9.0 to 1.9.1, which makes it compatible again. The commit for this is here: https://github.com/opdenkamp/xbmc-pvr-ad...2cb345f9c8
(Btw I am no where near an expert on Git, unix / linux etc - this was me just trying stuff and piecing things together)