TortoiseGitBlame doesn't work well with VirtualBox Shared Folders

What steps will reproduce the problem?

1. Host OS is Ubuntu, VirtualBox Guest OS is Win7.
2. "git clone" project under Ubuntu (or "TortoiseGit clone" under Win7, which makes no difference), and the whole parent dir has been shared to Win7 through VirtualBox's "Shared Folders" feature.
3. Under Win7, TortoiseGitBlame on any file.

What is the expected output? What do you see instead?

TortoiseGitBlame is expected to function normally, instead it prompts following dialog and refuses to work:

TortoiseGitBlame was already initialized for the repository "V:\projects\code\module-v3.2.0". Cannot switch to another repository ("V:\PROJECTS\CODE\MODULE-V3.2.0") at runtime.

What version of TortoiseGit and Git are you using? On what operating system?

TortoiseGit 1.8.15.0 (D:\Program Files\TortoiseGit\bin) git version 1.9.4.msysgit.1 (d:\Git\bin; d:\Git; d:\Git\etc\gitconfig)

Host OS: Ubuntu 12.04.4 LTS x64 VirtualBox: 5.0.0 r101573 Guest OS: Windows 7 SP1 32bit

Please provide any additional information below.