CSS from custom format retained in violation of formats configuration

[haugstrup]

Given a custom format that uses a custom HTML element, some styling will be retained from the custom format after deletion (but only in some cases).

Steps for Reproduction

1. Visit: http://codepen.io/anon/pen/bWpoZQ
2. Note that formats only contain our custom format and not e.g. background or bold
3. Note that the custom format has CSS styles applied
4. The editor has inserted our custom format and a space -- this could've been typed manually and marked up using a toolbar
5. Select all text
6. Type a single character

Expected behavior:
The editor should contain the single character and that character should not be formatted
OR
The editor should contain the single character and that character should be formatted using our custom format

Actual behavior:
The editor inserts the typed character, but some styling is retained from the custom format.

Retained formats: background, bold, italic and maybe more
Not retained: color

I shouldn't see background, bold, italic etc. applied because they are not whitelisted as approved formats in my Quill configuration.

Platforms:

Problem exists in at least Chrome, Firefox and Safari.

Version:

1.2.4

[jhchen]

This is a bug but I will note the workaround in the meantime, which is using quill.core.js instead of quill.js. This is because the normal quill.js build still registers formats such as bold, and relies on another mechanism (formats config) to disallow it, whereas quill.core.js has no knowledge of bold at all.

[benbro]

Related to #3988?