The post_modified / last_updated property of plugins gets bumped when you modify a plugin from within wp-admin - for example, closing the plugin.
That seems like a correct consequence.
Closing and reopening a plugin, or adjusting some details to it like committers, doesn't update the plugin itself. That should be controlled by the behavior of the SVN commits, not administrative tasks.
HOWEVER approving a plugin should change the update date :D Or at least it should change the publish date to 'now' instead of the date it was submitted so ​https://wordpress.org/plugins/browse/new/ shows the right data.
/browse/new/ is ordered by post_date which will always be the submit date at present, not post_modified which this ticket is specifically about.
My assumption here is that we need to store the submitted date as meta, for future use, and store the approval date as post_date instead.
Plugin Directory: The plugin post_type's post_modified date should only ever be changed in response to a SVN action, and not just because wp_update_post() was called.
This moves the code responsible for handling this special case from the plugin importer to globally affecting the site.
Plugin Directory: The 'post_date' of plugins should be set to the date which they first become active, this is when the plugin moves from approved to publish.
This ensures that the /browse/new view has the correct data.
Everything mentioned here should now be fixed.