use strict;
my $v = 'x';
print qq"$v{a}";
__END__
xa
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use strict;
my $v = 'x';
print qq{$v{a}};
__END__
Global symbol "%v" requires explicit package name at -e line 3.
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Note also that the interpolation code needs to make a decision on where the interpolated scalar ends. For instance, whether "a $b -> {c}" really means:

   "a " . $b . " -> {c}";
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or:

  "a " . $b -> {c};
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Most of the time, the longest possible text that does not include spaces between components and which contains matching braces or brackets. because the outcome may be determined by voting based on heuristic estimators, the result is not strictly predictable. Fortunately, it’s usually correct for ambiguous cases.

I don't see this as a bug. Remember that the right-hand-side of s/// is just a double-quoted string, subject to the usual interpolation rules.

The same disambiguation is needed in regular interpolated strings. Consider this snippet:

use strict;
my $var = "this";
print "$var{whatever}";
__END__
Global symbol "%var" requires explicit package name at -e line 3.
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use strict;
my $var = "this";
print "${var}{whatever}";
__END__
this{whatever}
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