Like one of the previous posts mentioned the /assist function will interveen and cause odd stuff to effect your castsequence.... atleast it did for me.

I used a castsequence on my 3xDPS and at one point they would fire of a wrath and stop casting..... I had a reset=target in my castsequence as the key to reset the castsequence. I got tired of them stopping sometimes and simply made 3 macros, starfire, wrath, moonfire:

(bear in mind im only lvl 47)

1:
/assist Focus
/startattack
/Cast [target=forcustarget] Starfire

The target=forcustarget is probaly redundant due to the assist focus arguement in the beginning of the macro.

The bottomline is I have left using the castsequence function. For my tank/spam macro I use the castrandom function.