A macro bug occurs when using the “?” variable icon with #showtooltip if switching between specs that do not have both of the spells listed in the macro. The macro icon becomes permanently set to the icon of the known spell instead of the "? variable icon.
Macro example, a very simply macro:
#showtooltip
/cast [nomod] Wild Growth
/cast [mod, @cursor] Efflorescence
I have this macro set to the “?” variable icon, and in Resto spec where I have both of these spells, the tooltip icon changes in conjunction with my mod key.
I switch to Guardian spec where I only know Wild Growth (and, notably, do not even use this macro on my bar). Since I do not know Efflorescence, the macro tooltip updates the stored icon to Wild Growth, overwriting the “?”.
When I switch back to Resto, despite regaining Efflorescence, my macro’s icon is still permanently changed to Wild Growth. I have to edit the macro and change the icon back to the “?” icon.
This is obviously problematic, as spec switches require a repair to macro icons each time.