Yes, telltales "acting up" in most context would be acting unstable, maybe pointing up, down, or even forward because of disturbed unattached air. The goal most of the time is to have them streaming back.
I found that adding leach telltales to my main was very helpful getting it trimmed. Especially after I started using a squaretop main which needed a lot different downhaul and traveler settings than I was used to on the H18 stock sails.