Has the lack of warnings on feature function ambiguity been fixed in more recent perl versions?

Nope

perl -wE " $x = q{txt}; sub ref {return $x . q{r};}; say &ref($x); "
perl -wE " $x = q{txt}; sub ref {return $x . q{r};}; say ref($x); "
perl -wE " $x = q{txt}; sub say {return $x . q{r};}; say &say($x); "
perl -wE " $x = q{txt}; sub say {return $x . q{r};}; say say($x); "
perl -E " say $^V "
[download]

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perl -wE ' $x = q{txt}; sub ref {return $x . q{r};}; say &ref($x); '
perl -wE ' $x = q{txt}; sub ref {return $x . q{r};}; say ref($x); '
perl -wE ' $x = q{txt}; sub say {return $x . q{r};}; say &say($x); '
perl -wE ' $x = q{txt}; sub say {return $x . q{r};}; say say($x); '
perl -E ' say $^V '
[download]

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$ perl -wE " $x = q{txt}; sub ref {return $x . q{r};}; say &ref($x); "
txtr

$ perl -wE " $x = q{txt}; sub ref {return $x . q{r};}; say ref($x); "
Ambiguous call resolved as CORE::ref(), qualify as such or use & at -e
+ line 1.


$ perl -wE " $x = q{txt}; sub say {return $x . q{r};}; say &say($x); "
txtr

$ perl -wE " $x = q{txt}; sub say {return $x . q{r};}; say say($x); "
txt
1

$ perl -E " say $^V "
v5.14.1
[download]

http://perl5.git.perl.org/perl.git?a=search&h=HEAD&st=free&s=say

http://perl5.git.perl.org/perl.git?a=search&h=HEAD&st=free&s=ambiguous

https://rt.perl.org/rt3//Public/Search/Simple.html?q=say

https://rt.perl.org/rt3//Public/Search/Simple.html?q=ambiguous