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This is related to: #1124
The fix works great when using the cancel button for a plugin within the page, but the issue still reproduces when a PlaceholderField is used in custom models (see: http://docs.django-cms.org/en/2.3/extending_cms/placeholders.html)
There's a lot of duplicated logic between plugin handling code in pageadmin.py and placeholderadmin.py and I think it's quite easy to fix one and forget about the other.
fixed with #1461