Columns don't provide a WYSIWYG experience in edit mode

[michitux]

Steps to reproduce:

Create a page with content

{{section}}
{{column width="33%"}}
Content in the column 1
{{/column}}

{{column width="33%"}}
Content in the column 2
{{/column}}

{{column width="33%"}}
Content in the column 3
{{/column}}
{{/section}}

Edit the page with the WYSIWYG editor.

Expected result:

The layout is the same as in view mode.

Actual result:

The layout is not the same as in view mode, the columns are displayed below each other, and there are several boxes with a lot of spacing displayed that make it hard to edit the page.