Since 2.3 the way that the cassequence reset has changed. Before 2.3 it was how long without a key press before the macro reset to the beginning. Now the macro will reset after that time regardless of its activity
can't test this, because I'm also at work (pst, don't tell), but I realy doubt it, because a change that would be that big (it would mean the 'holy grail' for every DoT Class, becasue if true I could make the follwoing makro for a druid:

/castsequence reset=18 Moonfire,Null
/castsequence reset=12 Insectswarm,Null
/cast Wrath

which would apply all my Moonfire after 18-seconds, Insectswarm after 12 and otherwise cast wrath.. ..this would be tooo good to be true ;)