Are new words supposed to appear in strengthen skills?
Since i don't know how to post images in the post, i'll simply transcribe the sentence that appeared to me.
Ili ankaû havas ruĝan Pomon -> they also have a red apple
The accent in the "u" is wrong, but i don't have it in my keyboard, so please forgive me.
The strange thing is that not only have i never seen the word "ankaû", but Duolingo also tagged it as a new word. And i was just practising!
Is this supposed to happen? Can i keep learning new words like this?
This is not supposed to happen. It's a site-wide glitch, not just related to the Esperanto course. I've had this happen a few times in the Italian and French courses (more so when I was still doing new lessons on mobile).
The word "ankaux" is in the first lesson of the skill Colors, which I see you completed already. What happened is that you finished this lesson without being asked a question with the word "ankaux" in it, but Duolingo still registered it as a word you learned. That's why it managed to come up in a strengthening practice. Somehow, it still recognized that you hadn't had a sentence with this word before, so it did highlight it as a new word.
Edit: also, you can post images with the code
!(http://example.jpg) (substitute a real image url, ending in .jpg/.gif/.png/etc, in the last set of brackets).