(2019-10-04)
By default Lastpass will be set to pre-populate username and password fields with login information if it recognizes the site and has credentials.
Most of the time, this is in fact what you want.
But.
If you were to, say, go to a Fortigate that you have the credentials in Lastpass for, then go to the Network -> Interfaces -> WAN{x} page… if that interface is a PPPoE interface, Lastpass will stick your firewall login credentials into the PPPoE username/password fields. So if you were to make an unrelated change, say enable/disable an admin service on the interface, and then click OK…
Pow, you’ve just clobbered the PPPoE credentials and the site is offline. And yeah I know that this happens because I did it this week.
So for your own protection I highly recommend that you go to the Lastpass Options (chrome: right-click on the Lastpass icon in the top right, select Options), and make sure that
Automatically Fill Login Information is cleared. It means you have to add two clicks to each login, but that’s better than accidentally clobbering things with inappropriate credentials.
Cheers