then start modify content of the first tab will cause next tab with
full-width filename render incorrectly (an empty column might appear).
It can be solved by switch to another tab, or press <C-L>, clear and redraw.
Please see the attachment to reproduce it.
1. vim -u NONE tabline_render.vim
2. :so %
3. :tabnew 中文測試
4. back to the tab "tabline_render.vim" and do some edit.
Before the tab "中文測試" should appear an empty column.
Tested on Unix and Cygwin.
And it looks fine in Vim 7.0 and 7.2.