I cast Vampiric Touch on my Cleric and after the turn after the first cast I was able to use it indefinitely. I was still limited by movement obviously, but it didn't use my action.
Edit: Just read the bug report format. I'll try to find my save, but IDK if I still have it. I remembered it was on a dwarven level 5 or 6 cleric (death domain). It was in the platform area just before you enter the old elven ruins near the end of early access. It was against a blood... something, undead creature with about 60 HP.