OK I think I finally nailed this problem by changing the timer settings on the vm - they need to come from the hardware timer and not be emulated. I haven't encountered the problem since

On Fri, Nov 29, 2013 at 10:11 PM, Kees Varekamp <kees@mroffice.org> wrote:

2 years ago, I had this problem that recordings would get badly out of sync. I've never been able to pinpoint the problem but found that the voip client's "preserve bandwidth during silence" setting made the problem go away.

But after moving to a new server, the problem has come back with a vengeance. And "preserve bandwidth during silence" does not seem to make any difference at all

The new server runs on vmware - which got me thinking that running on a vm perhaps could cause such a problem? 

Has anyone had similar experiences?