This can probably be best explained with specific steps:
1. Start learning Mining I
2. Pause Mining I / start learning another skill
3. Go to hardware vendor to buy a pick
4. In the vendor dialog, where it says "You need the skill Mining I to use this", click on Mining I
5. Try to learn the skill in the dialog box
The game seems to think that I'm already learning the skill, even though it's paused and I'm currently learning something else. It would be nice (and make sense) to have the option to resume learning that skill.
I also took a picture that kind of sums it up in all one go: imgur.com/31TqA.png