I applied 3.12 to both my Envoy and VP2 Console.
The Envoy is connected via Serial (w/USB adapter) and the VP2 Console via WLIP (and Weatherlink on WinXP).
I stopped Weatherlink in both cases and just as a precaution unchecked the "Upload to Weatherlink.com" box to minimize any potential conflicts on the WLIP Configuration webpage.
Afterwards, I had some issues with the old Windows XP box running Weatherlink for uploading to my web site. Weatherlink.com (and consequent CWOP and WU) were OK, but it was giving some timeout errors for uploads. The "bulletin", summary and diagnostics screens all worked OK.
I upgraded the Win8 machine (with the Envoy) to Weatherlink 6.0.3 before I ran the firmware upgrades. I tried upgrading the XP box Weatherlink as well and that seem to have fixed it. Started uploading, albeit with wrong times. I reset the time/date and all is well on both the Console and Envoy.
The Weatherlink 6.0.3 seems to be faster on the Win8 machine than the older version, but that is a subjective "seems".
Greg H