When I lock the screen in Gnome Shell, a shield screen appears when
hit any key (including e.g. Shift). This is good.
However, when the screen saver/monitor power save kicks in, but the
lock is set to a higher timeout, e.g. 30 minutes, no shield screen
appears after hitting a key. Instead, whatever key you typed is sent
to the application that has focus, but you can't know what application
that is ahead of time because the screen is in power save. I find
myself accidentally typing my password into random windows because I
assume the screen is fully "locked" but it is just in power save mode.
I.e. it is hard to distinguish between these two cases.
So why have you set the lock screen to a longer delay than your power save mode? By
default, the lock screen is activated immediately after power save mode kicking in:
Proposal: invoke the shield screen even when the screen isn't fully
"locked" yet, just in power save, to prevent keystrokes from being
erroneously sent to applications when waking up the screen.
That doesn't really make sense to me. You're basically asking for removal of the
the "Lock screen after blank for" option. If you don't like it, why do you
change it in the first place? Just leave it at the default value, which is doing exactly
what you're asking.