So, other wordprocessors have this feature, LibreOffice still lacks it it seems: When in a new empty document, you enter a small letter and hit spacebar, the letter will turn into a big letter automatically. Then if you hit backspace (to indicate to the processor that you don't want it to become a capital letter), the letter still stays capital letter instead of changing into a small letter upon backspace-input. Or is there a setting somewhere to set this behaviour?
No, in LibreOffice reverasal of auto-correction is done with <Ctrl>+Z For en-US local, the auto-correction table includes conversion of just "a" and "i", but user could define additional--and other locale have different auto-correction tables. => NAB, and no reason to change LibreOffice behavior.
Oh, and the uno:Undo command is dual assigned to <Ctrl>+Z but also to <Alt>+<Backspace> by default. You can change assignment through Customization dialog.