Searching around more on this issue, it seems to be a generic druids issue
but it might just be the blue hand cancel bug everyone is seeing, and it just comes up more often on your Swiftmend, the way it comes up more often for me on my power word: shield.
The solution suggested in that thread is to put
/use 2
at the end of your macro to immediately cancel the blue hand and it seems to work for some.

I found using:
and putting
/click SpellStopTargetingButton
at the end of my mouseover heal macros worked very well for me to get rid of this and not make me have to click twice to get rid of the blue hand and then cast the spell.