It looks like it is a problem with the git-cheetah extension with git 1.9.0.
https://github.com/msysgit/Git-Cheetah/commit/e7af79862b136efb414ac545f282939e2d290e3e
A recent change made for FarManager makes Git Cheetah capture stderr/stdout even when we are not interested in it, to avoid cluttering FarManager's precious console. Due to this workaround, Git Bash makes the Explorer -- Git Cheetah's primary intended consumer -- hang.
It looks like the fix has been commited to the codebase but as to when it will appear in the git update I have no idea!