Skype is proprietary software, so it can't be patched by open source
developers. There is not much interest in the open source community in Skype
because it is proprietary and there are several good open source
alternatives, so fixes are not going to happen. An explanation of the
problem is that Skype uses its own drivers and protocols and they are
incompatible with Ubuntu's. Sometimes the transition between the two is not
smooth.

Here is a page describing variouis Skype problems and fixes for Ubuntu:
https://help.ubuntu.com/community/Skype