I found a way to fix it, and it works perfectly for me.
Mkheffache, that's a bit of a hack! Good that it works for you, but I would still prefer an official fix from Skype.
When I replied previously that the update to a later version of Skype had fixed the problem, I spoke too soon. There is still a problem with it, but it's just not as bad. Sometimes it does and sometimes it doesn't. Weird!
The problem is not with the Skype app, it works just fine on Ubuntu with Unity. The problem comes from Cinnamon (I switched to Linux Mint a few days ago). Maybe it can be fixed on Skype, but this just works pretty well. I think the problem comes from Cinnamon, not Skype.