I've discovered while chasing other issues, that the window of opportunity for del to do it's job of taking you to bios is quite small.
If you start dabbing the del key too early, it gets ingnored and windows will boot.
If you start pressing too late, it brings up the tab menu.
The window of opportunity is only from the moment the full logo appears to system beep which is only about 1/2 a second.
For a single press of the del key at different times during post, here's what you get.
Before full logo, it gets ignored which is fair enough.
After appearance of full logo but before system beep it will take you to bios - all good.
After system beep it will be ignored.
For continuos presses of del at different times during post it's a little different.
Before full logo, it still gets ignored even though a press or two would have occurred between full logo and system beep.
After appearance of full logo and for any length of time thereafter, you will get bios.
After system beep you will get the tab menu - very odd behavior.
So this explains my problem with seemingly always getting eithera normal boot or the tab menu after I had turned off the full logo. I had no reference anymore [the appearance of the logo] as to when to first press del!
So it's not really a bug as such, just an annoyance. On all previous pc's I would just start dabbing the del key as early as I want or at any time so long as it wasn't too late and I would always get to bios.
This bios is timing critical and with the logo disabled, you have almost no chance of hitting the right spot.
If you turn full logo off, your better off using the F12 key. You can start pressing that immediately and for as long as you want and you will always get the boot menu with entering bios being one of the options.