Trade interrupts casting. Don't try to trade with someone in combat. It will interrupt any spells they are casting. Charm seems to have several bugs in it. The worst one is if you are charmed by an NPC, there is a bug where a random item in your primary weapon slot may sometimes change into something else.
Some people just die after being charmed.
Basically, be very wary when entering an area where you can be charmed or just avoid them alltogether. Fear can also cause many of the problems experienced with charm, such as the problem with your hot keys malfunctioning. Several bugs with pets seem to make the pet randomly disappear or go out of control. Levitation can sometimes cause you to lose control of your pet. Due to lag, you can still be hit by mobs after you think you have zoned.