Are your WordPress dashicons hip to be square, momentarily losing their icon appeal to a boring ole square…. after a period of time the icons in the WordPress dashboard become squares. Other icons in the dashboard are not affected because they use png images.
Interacting with the page again brings the icons back.
It seems to be a Chrome issue only, and is the font icon falling back to a fall back font which in this case results in a square. Chrome 33 looks to address this issue which is set to be released at the end of February.