Maybe it's intentional or also a bug, when i use the word bank it often suggests abbreviations like: f. m. and obl
Yes, I've also seen this quite a bit. I suspect this is because Duolingo has never been very good at presenting grammatical gender. Something that has remained a major flaw. The creators of this course have obviously attempted to do a good job at working around that, but as a result Duolingo is picking these up as real words when randomly picking words to present. That would be my guess, anyway.