ESC vs Meta for shifted keys

[Robert Pluim]

So Iʼve (finally) got an actual Meta key configured on my
keyboard. Iʼve always believed that Esc-as-prefix and Meta were
interchangable, but that doesnʼt seem to be the case:

C-h k ESC SHIFT <left>
=> ESC <left> (translated from <escape> <S-left>) runs the command
backward-word
C-h k ESC <left>
=> ESC <left> (translated from <escape> <left>) runs the command
backward-word
C-h k M-S-<left>
=>
<M-left> (translated from <M-S-left>) runs the command left-word

So this looks like emacs is not taking into account the SHIFT modifier
here? Or is there some default keyboard translation going on that I
need to disable?

Robert