From @nwc10

sv.c
6986​: sv_pos_u2b(sv,&append,0);

This means that calls to sv_gets() will fail for UTF-8 strings over 2GB, *if*
called in append mode, *and* the string wasn't UTF-8 encoded, *and* the file
handle is marked as UTF-8.

Append mode is only used in the core by the tokeniser, and for constructions
such as

  $a .= <FH>

Nicholas Clark

From @cpansprout

Exact copy of 72774.

@cpansprout - Status changed from 'new' to 'resolved'