Comment 13 for bug 728426

Ok, now I dug up a relevant link: http://www.dwheeler.com/essays/floss-license-slide.html

License compatibility doesn't mean they can be used interchangeably, only that code under one license can be combined with the other and relicensed without breaking the original license terms.

Basically, when you say that something is GPL-compatible it means that it can be merged into a GPL program, but it only works one way. (In favour of the GPL.) The merging goes MIT/BSD -> LGPL -> GPL, but you can't merge the other way. For Tomboy it's unproblematic to have MIT code in an LGPL program, but for us to have LGPL code in an MIT program is a problem.

Tomboy used to have the printing add-in (yes, some people do have their printing functions as extensions) under the GPL which worked because it was distributed alongside Tomboy but not integrated with it. It has since been relicensed as LGPL. (September last year.) If there was any GPL code inside of Tomboy proper it would have been a major problem and Tomboy would either have to strip it out or go full GPL.