That macro will use up 2 charges of Ice Floes if you press it multiple times. Use this instead:
#showtooltip Shifting Power
/castsequence [known:Ice Floes]reset=10 Ice Floes, Shifting Power, Shifting Power;reset=10 Shifting Power
Both require you to hit the macro at least twice but the 2nd macro will only use 1 Ice Floes charge and you can spam it. Not sure if there is a macro that requires only 1 press instead of 2.