If I use a macro such as this:

#showtooltip /use [mod:ctrl,@mouseover,help,exists][mod:ctrl] Flash Heal(Rank 7); [@mouseover,help,exists][] Flash Heal(Rank 4)

By default, the values for Flash Heal(Rank 4) is displayed. If I hold the CTRL key, the spell switches to Flash Heal(Rank 7) and those values are displayed. When I release the CTRL key, the values for Flash Heal(Rank 4) is displayed, but overlay-ed on top of Flash Heal(Rank 7), ie the values from Rank 7 is partially visible below the Rank 4 values.

I am using ElvUI action bars if that helps.

I'll have a look into this when I have the time!

Came here to say I'm getting the same issues as OP, also on ElvUI. unchanged bars. Something like:
#showtoolip /cast [mod:ctrl]Moonfire;[nomod:ctrl]Starfire
Will show both values once ctrl is pressed (and tooltip pic updates accordingly).

Should be fixed now with a new update. Feel free to reopen this if the issue perists.