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Changes between Initial Version and Version 1 of Ticket #28581, comment 4

initial	v1
3	3	I'm not entirely sure what `'click .preview': 'preview'` is for (introduced in [27499]). The Preview button on Themes screen doesn't have that class, and the button on Add Themes screen doesn't require that line.
4	4
5		It contributes to the issue, causing `themes.view.Theme.preview` to run twice on the same click, which in turn results in `themes.view.Preview.collapse()` running twice. Everything seems to work as expected without it.
	5	It contributes to the issue, causing `themes.view.Theme.preview()` to run twice on the same click, which in turn results in `themes.view.Preview.collapse()` running twice. Everything seems to work as expected without it.
6	6
7	7	`this.undelegateEvents()` prevents old callbacks from firing if you close the preview and reopen it. Otherwise `themes.view.Preview.collapse()` still runs multiple times.