IIRC there was something put out a while back that refers to the amount of DoTs a mob can have active on it. Something like a limit of 60 DoTs total but only 30 will show. It is possible that your DoTs are in the 31-60 spots, still ticking but just not seen. If they happen to be 61+ then they will definitely not show as they would not have even been applied.

After you toss out a DoT check your combat log to see if it was applied or if the floating text appeared confirming the application. I am curious though, since you have it set up to show only what you placed if the between 30-60 mark negates that option. Seeing as it doesn't show up on the boss, would it display for you. I am thinking not, since it is still calculated as 30+ and is programmed to not show.

Anyone else can chime in on this?