I can't find anything on this, but I'm not the only one this happens to.  I use Lync 2013.  I have multiple chat windows open (multiple tabs) and when I am typing in one window, Lync will all of a sudden switch windows so then all of a sudden, I'm typing in another window!  It's very annoying!  It's not only when I'm typing either.  I could be just viewing a chat window, and Lync will decide to just switch what chat window I'm viewing.  This happens to everyone in my organization.

Anyone know what causes this or how it can be fixed?  Anyone know what I'm talking about?

I've never heard of that, but it's not a client feature.  Do you have any touchpads or anything that might be overly sensitive?  Do you have different types of workstations connection or are they all the same make/model? 

Ensure Lync and Windows are both fully patched in the meantime.  See if you can replicate this on a clean Windows image without any additional software installed.

This literally happens to me daily... It's the most frustrating thing ever. It happens to a lot of people that I work with as well and literally watching it happen on my other monitor as I'm typing this.

I'm fully updated and patched and running Windows 10 Pro. Did the same to me on a separate install on Windows 7 Pro and also happens on my laptop running Windows 8 Pro.