It would seem to me that this is a bug in Parse::HTTP::UserAgent. It contains a regular expression to suppress those messages, but the RE is

use constant RE_WARN_INVALID  => qr{\QVersion string .+? contains inva
+lid data; ignoring:\E}xms;
[download]

... which will quotemeta all metachars, especially .+?, which seems wrong. Also, the mixed usage of x and \Q happens to work but usually when using /x, you should use \s (or [ ]) for matching spaces.

My approach would be to either preload and monkeypatch Parse::HTTP::UserAgent::Constants or to fix the module upstream.

Also, I'm not sure what actually raises these warnings.