Couldn't they have just been wedged in there tight enough that they weren't able to float?
Ice melts in liquid. And the sides of a glass are smooth (and I don't remember if the glass was straight or angled). I would think that pretty quickly whatever ice was "wedged" would be melted and the cubes would float to the top.
And doesn't ice under pressure melt a little? That's what happens under ice skates?
They were underwater for sometime. And it was like two of them.
They were plastic.