There is a major issue with current Blizzard raid frames as well as party frames when you have the raid frames enabled for party.
When you have someone in your part/raid targeted and then switch to a new target and start healing, the heal is NOT targeting the new person you targeted, it’s either healing the old target or yourself.
It appears to be happening completley randomly but this is a HUGE issue as a healer that you can’t reliably heal who you want to with these current frames. Was never an issue before last Tuesday and the UI changes.