That's ok, I have meanwhile refactored everything* into a MessageData plugin anyway so the plugin will work** even if the dialog is closed.
*Everything except for timer stuff, which for some reason works differently for a dialog than for a message plugin.
**There are some strange effects like hanging or crashing application on Close, when the dialog is in certain states. I will need to investigate whether this is an effect of the missing CoreMessage calls or something that happens now due to refactoring.