[exim] unknown routing option or transport name /w manualrou…

I have an issue with a manualroute router. This router (below)
uses a mysql lookup to return the host to route to. It works 99% of
the time, however sometimes and seemingly with messages containing
multiple recipients, I get the following error for 1 of the recipients:

2005-10-19 13:14:37 1ESDm9-0006Nr-KQ Error in to_mailbox router:
unknown routing option or transport name "host.from.db"

host.from.db is exactly what SHOULD be returned from the lookup, and
is the same value returned for the other recipients that were
delivered properly.

The router looks like this:

to_mailbox:
     driver = manualroute
     condition = ${lookup mysql {SQL_Q_USER} }
     transport = remote_smtp
     headers_add = "X-COMPANY_NAME-Gateway: true\n"
     route_data = ${lookup mysql {SQL_Q_MBOXROUTE} }

The condition works fine and returns 1 or 0 depending on if the
local_part/domain exists in the db

If I replace the route_data with:

     route_list = * host.from.db

It ALWAYS works...

Any thoughts would be appreciated, this is confusing the hell out of me.

Thanks in advance,

-jwb