I ran into the same issue....I think.
I did a couple of recent installs using the latest downloads. The global setting is derived from the initial installation steps of the software as it asks about the TZ. In my case, it only involved the Yealinks as I was using T48. If you go to troubleshooting and parameters it may show how the system accommodates each make. In my case, the system had the correct parameters for every make but the Yealink. I was installing on the US East Coast (-5) and the Yealinks had Athens Greece. Fortunately, it was a coupleof hotel installs with only a few T48s, so it was no big issue to change in the provisioning of the phone,,,,,,,,
but I am (somewhat) glad that someone else may have run into the same issue. I checked my own system and it was fine, but then it was migrated and updated from earlier versions, so am uncertain at what point the issue came about or what caused.
BTW, I do not know that changing the parameter for the Yealink fixed the issue. I was on a tight schedule and did not test it; just changed it in provisioning.