Plot directive may be confused by ..include:: #17860

Bug report

In our docs, we have users/whats_new.rst that does .. include:: prev_whats_new/whats_new_3.3.0.rst.

For any plot directives, this latter file creates files like build/plot_directive/users/prev_whats_new/whats_new_3-3-0-*.*. Somehow this also gets copied to build/plot_directive/users/whats_new-*.*. Then in the final docs (in build/html), this ends up in coming from _images/whats_new-*.*. I don't really understand why that third copy is made, since the other two still exist in build/html, but whatever.

The problem occurs when you update plots in whats_new_3.3.0.rst. Only the first image is updated, and nothing is copied to the second or third locations.

Matplotlib version

• Operating system: Fedora 31
• Matplotlib version: master (actually, head of Refresh what's new page for 3.3.0 #17858)
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg
• Python version: 3.7.6
• Other libraries: Sphinx 3.1.2