Steps:

1. Enable 2017 Editor in beta features, and make sure you enabled "Syntax highlighting";
2. Open random categories, e.g. https://en.wikipedia.org/wiki/Category:Beijing_Subway_line_templates;
3. Click Edit source

Actual results:

Source codes are white, but then by clicking read and re-click Edit source, they shown as well:

Expected results:
I should be able to just show colored source codes, just once.