The original Flagbearer text tried to constrain the target selection for
   spells and abilities that could target them, but it was unclear whether
   that constraint also affected spells and abilities that change targets.
   Nowadays, the wording is clearer:

   Standard Bearer  {1}{W}  Creature - Human Flagbearer  1/1
/ While choosing targets as part of casting a spell or activating
   an ability, your opponents must choose at least one Flagbearer on
   the battlefield if able.

   This no longer triggers and ends up with targets changing, it just adds
   in the constraint the way the original text tried to.