But you don't *always* get the deprecation warning:

C:\>perl -le "$_ =~ /{}/;"

C:\>perl -le "$_ =~ /.+{}/;"

C:\>perl -le "$_ =~ /a+{}/;"

C:\>perl -le "$_ =~ /(a+)?{}/;"

C:\>perl -le "$_ =~ /a{}/;"
Unescaped left brace in regex is deprecated, passed through in regex; 
+marked by
<-- HERE in m/a{ <-- HERE }/ at -e line 1.

C:\>perl -le "$_ =~ /\d{}/;"
Unescaped left brace in regex is deprecated, passed through in regex; 
+marked by
<-- HERE in m/\d{ <-- HERE }/ at -e line 1.

C:\>
[download]

That behaviour fits ok with the (undetailed) documentation that Athanasius found, but does it tie in at all with the cases you're describing ?
(I don't see the connection, though that doesn't mean there isn't one :-)

Cheers,
Rob