typeset -u (for uppercase) and others like -LRZul don't apply to
(associative) arrays:

$ typeset -au a
$ a=(a)
$ echo $a
a

Just as well IMO as it would cause confusion with -U, or worse
for the keys of associative arrays. People can (and probably
should always instead of using those ksh-style flags) use
parameter-expansion-flags instead (${(U)array}...).

Other option is to go the ksh93 way:

$ ksh93 -c 'typeset -a -u -R3  a; a=(a b); printf "<%s>\n" "${a[@]}"'
<  A>
<  B>
$ ksh93 -c 'typeset -A -u a; a=([a]=x [A]=y); for k in "${!a[@]}"; do printf "%s => %s\n" "$k" "${a[$k]}"; done'
A => Y
a => X

(for associative arrays, only the values are transformed, though
for elements whose values are arrays, that doesn't apply to the
values of those arrays:
$ ksh93 -c 'typeset -A -u a; a=([a]=x [b]=(n m)); echo "${a[a]}" "${a[b][0]}"'
X n
).


Doc patch attached for the current situation. I'd say it's
probably not worth mentioning that in the case of arrays tied to
scalars (typeset -T), only the expansion of the scalar one is
affected.

-- 
Stephane