[kaev]

When you root a mob that is running full speed (i.e. agro'd on you and charging), DoT damage will often (always?) be at the reduced (moving) rate. Rerooting the mob does not fix this. It doesn't matter if the DoTs were already on the mob or are cast after it is rooted.

The only fix I've found to this in-game is to engage the mob in melee after it is rooted. Alternately you can root it while melee'ing to avoid trigering the bug [edit](Is not a problem if the mobs can be rooted in place and don't need pulling, until of course you get a root break and the mob charges you.) [/edit] This is obviously NOT an ideal tactic for a druid as at higher levels dual-wielding mobs are able to vaporize you in seconds.