EDIT: Response to Lene's provided link. For some reason, I thought it was the last post in the thread... sorry for the randomness.
An interesting read, indeed...
1. The article is trying to sell you something. "The license allows you to use midi-LOOPs with your personal computer applications and. explicitly allows the use on your personal website, so you can include midi-LOOPs under this license in all your personal Webpages." This shows more than a randomly placed period-- it shows that the author is clearly trying to persuade rather than inform.
2. The article only addresses midis created by musicians. "This applies also to MIDI files where the creator - the recording musician - does not make any money." Note that when they refer to "stolen", they put quotation marks around it. It's not talking about remixes.
3. The article clearly wants you to scare you.
Only a virtual artist lives from honour and fame alone, real humans need cash to pay their bills, so be careful, if it is called "free" (or available per anonymous download ) - if it does not come from the copyright owner ( as DEMO) or under and with a stated license, it could be "stolen goods" - and a bill (copyright fine) could follow the trail to the "reckless" creator and the "unaware" user!
Note the use of quotation marks to show that it's their words, not the copyright law's.
And, I do believe the article's initial assumption to be incorrect: "MIDI files are another form of recording music -sometimes even referred to as 'digital sheet music'.Therefore they constitute a new creation or a use of music like printing sheet music, performing music, or recording on tape". Right, some people refer to Midis as "digital sheet music", so clearly it must be illegal.
Ultimately, I think the article is pretty clearly trying to sell you on their product. If they were a neutral source I'd offer them a little more credibility, but even then they don't exactly clarify or back up their position very well.
Just my 2 cents. ;-)
Double Edit: Khengi, it's 100% legal to use music you created in your game. Even if someone else made it, as long as you own the license and/or copyright, it's fine.