I find that wiggly surfaces wiggle with seemingly unrelated changes. I just saw one of my surfaces go from 0.0degrees off tangent to 2degrees with a simple 0 offset. If the hole needs to be circular I would add it as far down the tree as possible. I hope this helps.
Not an answer but a workaround:
Sketch the final size hole.
Untrim the hole to patch it up.
Use the sketch to trim the new hole.
I expect this to be a correct behavior as you're extending the surface mainly in linear direction. So best might be to use what Kieran has suggested
Draw the final circle and use either loft or if possible planner surface to fill the gap.