Border-radius delay on hover

Border-radius takes a half-second or so to load on hover, so square div is shown before it corrects to the corrected rounded shape.

Code works correctly in Firefox, but does not work on Safari or Chrome.

Here's the link. Hover over any of the 3 circles to see the bug in either Safari or Chrome.

http://ift.tt/1CEAXV3

Why is there this delay?

Thanks!