Hesse actually fixed that in the latest SVN. I had the same problem, but can now type in 247 and actually get channel 247 (TBS, in my case) in my directv lineup. It doesn't add dummy channels, but actually fixes the problem entirely. Just uncheck the "select by index" option and it will work exactly as you are describing.
Awesome! I am running mediaportal-svn--09-24-2006--02-04-rev10448 ATM and I'm guessing it's in this SVN:
In the changelog I guess it would be this:
23/09/2006 [11:27h] mPod added: "Select channel by index" did not work in TVGuide and everywhere for External Channels (thanks to Hesse)
I'll have to make sure the "select by index" is unchecked with my SVN installation. If this is the case, then this plugin created by Hesse will make things SOOO much easier!
One other question, and I hope I don't take things too far off topic for this thread, but how fast/slow does one have to enter in channel numbers with the MCE remote? I find that the faster, the better, but this doesn't seem right