Strange issues with garage band 10 and sound fonts sf2

Actually, you can't. The linked article specifies exactly that you can't:

to create your own original music compositions or audio projects. You may broadcast and/or distribute your own music compositions or audio projects that were created using the Audio Content, however, individual audio loops may not be commercially or otherwise distributed on a standalone basis, nor may they be repackaged in whole or in part as audio samples, sound effects or music beds."

(emphasis mine)

You can create as many songs as you want using all the sounds you have in the loops and sell the songs. But you will be packaging the sounds (or repackaging) as audio samples of your application which seems to be forbidden.

whenever I record audio in QuickTime

This is the problem. QuickTime doesn't offer the ability to change the recording type or to pan inputs to a particular track in the recording when you're making it. It records stereo. And it captures one input left, the other input right. I just tried it out with my Duet and, no matter where I set the pan on the mic input in the Maestro mix console, QuickTime captured that signal input on the left channel only.

The solution, I'm afraid, is to stop using QuickTime.

Garageband, which is likely already on your Mac, will let you capture a mono source and then pan and bounce a master mix with the mono source placed in any location you like in the stereo field. It definitely is a more suitable interface for capturing and manipulating audio than QuickTime.