This happens with posh-git 1.0.0 beta, and possibly earlier. We have the following lines in the psm1:

if (!$Env:HOME) { $Env:HOME = "$Env:HOMEDRIVE$Env:HOMEPATH" }
if (!$Env:HOME) { $Env:HOME = "$Env:USERPROFILE" }

This is a problem if the HOME variable wasn't previously set, as it may affect various unrelated programs.

In our particular case we have USERPROFILE pointing to the local C:\Users\name as usual, and HOMEDRIVE set to a mapped network drive. Some programs might default to HOME, then USERPROFILE then HOMEDRIVE, which is now reversed after posh-git has been imported.

posh-git shouldn't mess with important environment variables that affect other things than Git.