grout popping off the wall

[bob_jenkins]

I have a shower in my new house with 6"x6" ceramic tiles with 9x9

2/3"x2/3" glass tiles interspersed. I sealed the grout with Tile Perfect Stand n' Seal Grout Sealer. About 20 minutes later, I heard "tink .. tink tink .. tink" and saw that the grout was popping off the wall around the glass tiles. Has anyone else had that happen? Any idea what caused it?

Now that some of the grout's gone, I can see the glass squares have some thick soft plastic backing (silicone?) to bring them up to the same level as the thicker ceramic squares. Grout came off around all the glass squares, and between the glass squares and the ceramic squares, but all the grout between ceramic tiles is fine. The grout between glass tiles, and between glass and ceramic tiles, is shallower because of the plastic backing. This is the first time the grout has been wet that I know of since it was installed; I hadn't put water on it before I put grout sealer on it. The grout is dyed blue, but I doubt that's relevant, because the grout between ceramic tiles is fine and it's all the same grout.

[JoeSpareBedroom]

Do the instructions for the sealer recommend waiting any particular length of time for the grout to age, before applying the sealer?

[bob_jenkins]

I didn't see any. It's been over a month since the grout was applied, so I doubt that's it.

I notice I have three rows of the same glass tile elsewhere, with a different grout, that wasn't affected. Don't know what backing those have, if any. So the grout sealer + glass tiles alone aren't the problem.