It seems gvim is not playing nicely with tiling manager. I encountered this bug.
It seems I am not alone with this problem. To maximize and restore the window each time doesn't seem to be a good workaround. The workaround I used are from the stackexchange, add the following line into my .vimrc:
set showtabline=2It always display the tab bar. Although it wastes some spaces, it gives me a proper displayed window.