I have this problem too and patched it like this.
You have to run the following command in TVHeadend's /share/tvheadend/src/webui/static
cp tvh.js.gz tvh.js.gz.orig; gunzip -c tvh.js.gz.orig | sed 's/RegExp.escape(r.get(this.valueField))/RegExp.escape(String(r.get(this.valueField)))/' | gzip > tvh.js.gz
If something goes wrong copy "tvh.js.gz.orig" back to "tvh.js.gz".
Edit: The above line has to be on one line of course. Unfortunately the Browser breaks it up.