Frozen screen at the end of a skill
This has happened to me randomly three times in the past two days, always with a bonus skill (Flirting), both in Italian and French. After answering all the questions and expecting an acknowledgement of a completed refreshment of a skill, I wait for minutes and nothing happens, the final 'O' in the Duolingo heading does not show circling movement. When I press the Home button, I get a warning that all work will be lost, but after a few minutes waiting I went back to the home screen and started all over again. On every second try it has worked.
I use the latest OSX Mavericks/Safari on a fairly new iMac. The internet connection is always good as I can freely load pages in another tab.
p.s. I have never seen the 'grading' message on the OK button before, the system seems to be slower than usual.