"this requires installation of untrusted packages": incomplete warning, then "OK" button does nothing

Additionally, the Settings button leads to a Tab in Settings where there's nothing related to trusted/untrusted packages.
Ther relevant tab is Authentication, but you have no clue of what you are supposed to do there, because
- the error message didn't tell anything about what are the problematic untrusted sources that allegedly are required
- there's no option to "allow untrusted sources" or anything like that, so you should magically know which source you would need to add

And most important, Update Manager should at the very least let you install ALL OTHER updates except the ones that are causing the issue, so at least one would be able to isolate them.

Altogether this is designed in the worst conceivable way.

The only way out is to check only one update (of the several-dozens list), install it, and then again with the next one, until you find the one that is causing the wrning.

Or a few at a time, or half of them in a bisection-search-like fashion.
Totally ridiculous.

And finally, by "bisection", I identified the package which was causing the warning: tortoisehg (or some of its dependencies).

I had installed this package with "sudo apt-get install tortoisehg".

So now I ran "sudo apt-get install tortoisehg" from a command line and I got this prompt:
WARNING: The following packages cannot be authenticated!
  tortoisehg mercurial mercurial-common
Install these packages without verification? [y/N]

Why on earth doesn't Update Manager just give the same prompt and the same Yes/No option? That's the issue.

I'll change this to Verified because I think the source of the issue is pretty clear and it's nonsense to wait for some other random person to stumble into the problem, wnich is easily reproducible.

I meant confirmed

I've just had the same as Teo - the update was for Thunderbird and one file for Ubuntu base only

So, following Teo's suggestion I unticked the Thunderbird files and just left the base file

EVERTHING was installed without error

When I said EVERYTHING, I meant all files including the unticked Thunderbird ones

Just had another example - update was for Ubuntu base only - got warning message, clicked OK and ran the updater again - ALL OK

Another update - icon for software updater is green - update for ubuntu only - install - fail

close updater - open it again - all lists are refreshed - list of updates appears - install - ALL OK

I also had that problem, updater closed by clicking ok. No info what was wrong.
After reading Alex's posts (#8 and 9), I manually started updater, and it worked for me.

Update manager installs a range of items and concludes and immediately update manager pops up with another install, this time for a small item for "ubuntu base". I accept, it asks for my password which I enter and then a panel pops up saying "this requires installation of untrusted packages" (which is the same as what started this bug report.

Note that at that moment the mouse clicks are not effective (a separate bug, it seems to me).