(Needs confirmation) When updating plugins, WordPress won't update any new plugin updates that are found

[pikamander2]

On a number of occasions, I've noticed that when I go to wp-admin/update-core.php and tell it to update my plugins, the system will:

1. Update most of the plugins
2. Report that all the plugins were successfully updated
3. Still report that a few plugins need to be updated

That's very confusing to end users, because how can there be more plugin updates if all of their plugins were supposedly just updated?

I've seen that bug happen many times, but only just now did I notice something else; after you click the "Update Plugins" button, the little orange notification number will sometimes increase after a second or two. That makes me think that the update function is checking for new updates but not adding them to the list of plugins to update.

Since the only plugins that get updated are the ones that were "checked", it does make sense that new updates wouldn't automatically be added. That said, the process still seems clunky overall.

Maybe it would be better to check for updates before the wp-admin/update-core.php page loads? That way the user would be presented with the actual list of plugins that need to be updated, rather than a partial list. It would block the page load for a few seconds, which is undesirable, but in most cases I think that would be a better behavior that the current one, which occasionally requires you to update your plugins twice and gives little explanation of what's going on.

Note that there's a lot of partial speculation above, and the nature of this issue makes it hard to consistently reproduce.