Description

Most templates you can copy-paste as plaintext wikicode and paste into VisualEditor. Pasting the plaintext "{{cn}}" into a VisualEditor document will result in the wikicode "{{cn}}". The same applies to all article cleanup templates and infoboxes.

However, if you paste in the plaintext string "{{dab}}", the result will be the text contents of the page Template:Disambiguation, namely "{{Dmbox|type=disambig|text=<includeonly>{{#if:{{{nocat...". The same applies to {{db-a7}}, the result is just the raw content of the template page itself.

This is quite confusing since there are no clues left to the user that they haven't actually transcluded a template. Some articles have had an accidentally expanded speedy deletion template on them for 6+ months (example 1, example 2)

I have not been able to figure out what exactly differentiates un-copyable templates and copyable templates. Templates based on Template:Dmbox are un-copyable, while templates based on Template:Ambox are copyable.

How to reproduce

Paste the plaintext string "{{dab}}" into an English Wikipedia sandbox and see the resulting wikicode..

Expected behavior

The plaintext string "{{dab}}" should be the wikicode in the saved page

VisualEditor is clearly able to add this template since if you go to Insert > Template > dab, the correct wikicode is returned.

Previous related tasks

The only related topic to this I could find was the 2013 regression T56410.