Use of ":" in a Parameter for a HTTP request

Hello,

I tried to add a Test Step for the following HTTP Request:
/cgi-bin/readnow.xml?TYPE=Meter&ADDR=9555444&OBISID=8-0:1.0.0&ACTION=Last HTTP/1.1

TYPE, ADDR, OBISID and ACTION were successful extracted as parameter out of the Endpoint URL.

But soapUI sends out:
/cgi-bin/readnow.xml?TYPE=Meter&ADDR=9555444&OBISID=8-0%3A1.0.0&ACTION=Last HTTP/1.1

Any idea why the character ":" in the parameter OBISID is changed to the ASCII hex string "%3A"?

This appears in soapUI Version 3.0.1 as well as in 3.5-beta1