Mirror Blade "bounces" hit same target
Mirror blade has always been able to hit the same target more than once… so this isn’t a bug. It has 4 bounces, which means it can only hit the same target up to 3×. So, if you had checked your log, you would have seen it hit you 3x and your pet x2 if it was standing ‘right next to you’ like you say. If your pet didnt take any dmg then that means it probably bounced back to the mesmer x2 providing them with might.
Four ‘bounces’ = Five hits total. The first hit doesn’t count as a bounce.
Mirror blade can bounce of you, since it gives buffs to allies. others, such as rangers richochet, engi static shot, thief trick shot, can only bounce off enemies since they are purely offensive.
Engi elixir F bounces off allies. Static discharge does not.
Mesmer winds of chaos staff 1 also bounces off allies and enemies.