Yep. A limitation of that syntax is that, whilst the hash is a constant, it contents are not.

[14:26:14.28] c:\test>p1
use constant HASH=>{ a=>1, b=>2 };;
print %{ +HASH };;
a 1 b 2

HASH->{ c } = 3;;
print %{ +HASH };;
c 3 a 1 b 2

delete HASH->{ $_ } for keys %{ +HASH };;
print %{ +HASH };;
[download]

That can be solved using the same Hash::Util::lock_hash() method I mentioned above.