guifontwide not work until manual reload vimrc

Version

VIM - Vi IMproved 8.1 (2018 May 18, compiled Aug  3 2018 05:14:32)
macOS version
Include patches: 1-235
Compiled by travis@Traviss-Mac-1044.local

Steps to reproduce

1. add guifontwide setting to .vimrc set guifontwide=<FontName>
2. reopen MacVim, typing any double width character
3. reload .vimrc by source $MYVIMRC

What is expected

The double width character is exactly the font I set before or after reloading .vimrc

What is actually happening

The font only display correctly after reloading .vimrc

Example:

my setting

after reopen macvim

then reload vimrc

Reproduce the behavior in MacVim using the .vimrc setting set guifontwide=<FontName>, then compare startup behavior with reloading via source $MYVIMRC. Trace how guifontwide is applied when MacVim opens and when the vimrc is sourced; done means double-width characters use the configured font immediately after reopening.