This thread is over a year old but figured I'd post a reply anyway in case someone else comes across the same problem...
The problem is that some of the pages in
\Inetpub\vhosts\webmail\horde\services\portal
get replaced with near empty files containing nothing but the word 'fake'. A quick fix is to copy the appropriate files from
\Inetpub\vhosts\webmail\horde\templates\portal
over the 'fake' ones. Dunno about a "real" fix though...