Another solution would be to use
-webkit-backface-visibility: hidden;
on the hover element that has the opacity.
Backface-visibility relates to transform
, so @Beskow‘s has got something to do with it. Since it is a webkit specific problem you only need to specify the backface-visibility for webkit. There are other vendor prefixes.
See http://css-tricks.com/almanac/properties/b/backface-visibility/ for more info.