new gnumeric
ensure the long format toolbar is visible
A1: xyz
select the x and click on the subscript button
the x becomes subscripted (good)
select the z
the subscript button is still marked as depressed (bad!)
click on the subscript button once
the z does not become subscripted (bad!)
note that the subscript button now does not look depressed (at least consistent with the state of the z)
if you click the subscript button again, the z becomes correctly subscripted.