I looked into this further and was able to reproduce the issue using your code, and find an explanation and workaround. glob in scalar context acts like an iterator. However, the iterator state is attached to the glob call site, even when the argument to glob changes. Here's a simple way to reproduce the issue:

$ touch foo bar
$ perl -MData::Dump -e '
  sub myglob {scalar glob($_[0])}
  dd myglob($_) for qw/foo bar/   '
"foo"
undef
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One might expect the output here to be "foo" and "bar". There is an excellent discussion in RT#123404, and it doesn't sound like this behavior is going to change, as potentially confusing as it is.

A simple workaround is to force list context:

return if ()=glob("$directory/*");
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