In general I find it very odd for a company to change the favicon for a domain or site since it's meant to aid which recognition of what tabs go with what sites you are familiar with. Putting an icon that is unrelated to your own logo destroys the ability for the user to recognize their gmail tab quickly. At best, their intent could be that this is meant as a placeholder favicon until the user sets his/her own custom one. But even in that case, I'd except the regular Gmail favicon until the user feels compelled to seek out this configuration and set it themselves.