Combat while riding

You can trigger dungeon switches and do normal attacks, the highlighted skills are probably the skills that the pet has and that wouldn't be a glitch

I can't do normal attacks outside of hitting dungeon switches though you make a good point

If there's skills lit up while your mounting the Sheep Nimbus but you can't load/use them, then it's probably glitched. Might just want to file a report to Nexon forums anyway.