When quoting a reply that contains a heading, the heading syntax gets rendered as plain text. This is presumably caused by the leading space. Note below that even when stripping spaces manually, ## still gets interpreted wrongly if a bullet list follows.

Example text.

== heading

• Foo

## heading

• Foo

Quoted (default):

Example text.

== heading

• Foo.

## heading

• Foo.

> 
> Example text.
> 
> == `==` heading ==
> 
> * Foo.
> 
> ## `##` heading
> 
> * Foo.

Quoted (strip leading spaces on headings):

Example text.

== header

• Foo.

1. ## header
2. Foo.

Quoted (strip all leading spaces):

Example text.

== header

• Foo.

## header

• Foo.