What Giantslayer said is right but I found a way to avoid this split second breaking the priority spells.

You just have to add more Stone 3 and Stone 2 so that you can still "spam" the macro without any issue, something like that :

/ac "Stone III" <t>
/ac "Stone III" <tt>
/ac "Stone III" <t>
/ac "Stone III" <tt>
/ac "Stone III" <t>
/ac "Stone III" <tt>
/ac "Stone II" <t>
/ac "Stone II" <tt>
/ac "Stone II" <t>
/ac "Stone II" <tt>
/ac "Stone II" <t>
/ac "Stone II" <tt>
/ac "Stone" <t>
/ac "Stone" <tt>

I can't assure it's 100% reliable but I had no fails for a while now that I can easily say it's around 99%.