NCV - problems setting to GAUGE

I defined an NCV as type GAUGE:

$ tail -1 hobbitserver.cfg NCV_modjk=modjk:GAUGE"

But when I actually peek at the rrd file, it sys it is type DERIVE.

<!-- Round Robin Database Dump --><rrd> <version> 0003 </version> <step> 300 </step> <!-- Seconds --> <lastupdate> 1159488942 </lastupdate> <!-- 2006-09-29 00:15:42 GMT -->

    <ds>
            <name> modjk </name>
            <type> *DERIVE* </type>
            <minimal_heartbeat> 600 </minimal_heartbeat>
            <min> 0.0000000000e+00 </min>
            <max> NaN </max>

Any idea what could be the issue? I tried deleting the rrd and letting hobbit recreate it, it was again created with DERIVE type