Thin grey strip inside border when using WSL + GUI App + Vcxsrv

I've been using emacs inside WSL and vcxsrv to display the interface. One small issue I found with this approach is that there's a very thin grey area between the border and emacs's text area. Please check a screenshot below. I've tried Windows native emacs and found that it doesn't have this issue. I've also tried running xfce4-session(in WSL) and then start emacs from inside the session, it also doesn't have the issue. Does anyone have some ideas on which part this is related to? Emacs, WSL or vcxsrv? Is there way to remove this grey area?