WYSIWYG Markdown editor - nested blockquotes cannot be pasted

To reproduce issue, do the following:

1. Copy the following Markdown code:

> > This line will not appear when pasted

> This line WILL appear

So will this line

2. Open the dialog to create a new comment on an existing issue, or create new issue.

3. In the editor box, paste the code you copied, noting that the first line (starting with ‘> >’) does not appear.

Operating systems:

• Windows 7 Enterprise
• Windows 10 Enterprise

Browsers:

• Firefox 67.0 (Quantum)
• Firefox 60.7.0 (ESR)
• Chrome 64.0.3282.167
• Chrome 73.0.3683.103

I don’t strictly expect nested blockquotes to render as nested blocks (a leading literal ‘>’ within the block would be just fine) however, it’s a gotcha when pasting markdown from a separate editor that it will (partially) fail silently, and leave parts out of the paste, as these could fairly easily go unnoticed.