The issue looks similar to 1330794.
When the current theme is sub-theme and option "Use theme CSS" is on, only sub-theme CSS is loaded in editor (CKEditor in my case), but not the base theme CSS.

Configuration:
Base theme - Bootstrap
Current theme - custom theme based on Bootstrap CDN starterkit
Admin theme - Garland
Theme for content editing - the same as current (Use admin theme for content editing is set to No)

Comments

Aracon created an issue. See original summary.

TwoD’s picture

Status: Active » Closed (duplicate)
Related issues: +#2289683: Select in-editor theme and get all stylesheets

Please try the patch in #2289683: Select in-editor theme and get all stylesheets, the approach used there should make sure all stylesheets are included.