Killing the xwidget buffer doesn't turn off minor mode

[cfclrk]

When markdown-xwidget-preview-mode is enabled and I kill the xwidget-webkit buffer (say, by just doing a C-x k in that buffer), the xwidget-webkit buffer is killed, but markdown-xwidget-preview-mode remains enabled.

So, if I make a change to the markdown file and save it, a new xwidget-webkit buffer pops up.

Ideally, explicitly killing the xwidget-webkit buffer should disable markdown-xwidget-preview-mode in the corresponding markdown buffer.