XML extensions can disappear on disable

Here's the description, copied from Slack.

vincent:
I am having a weird thing with my Studio project:

• create a new XML extension
• put some XML and save
• click the `disable` button and wait a few seconds
  The content of the XML extension gets deleted. It does not seem to impact old XML extensions, only new ones. Can someone else try to reproduce?

stuart:
I don’t observe this. I am able to disable and re-enable a new extension
stuart:
correction: in that exact order I DO see what you see.
stuart:
if you leave the extnsion after saving though (navigate elsewhere) then return and disable it, it’s intact.