Sometimes I use the following method for debugging hard to track warnings (there's actually a Log4perl-compatible object instead of print there, use whatever fits you):

use Carp; 
local $SIG{__WARN__} = sub { print( Carp::longmess (shift) ); };
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This is a "trick" however and should be agreed upon by the rest of the team. See also this node for sigwarn/sigdie explanation.