Landscape Spline always updates the Landscape

The Landscape will always be edited by splines even if you have not pressed Apply Splines to Landscape. This has a disastrous effect on performance and is extremely annoying.

It wasn’t like this before. When did the specs change? This is a terrible feature to say the least, and it’s a major obstacle to creating levels.

I want to go back to the previous method of adjusting to the landscape at any time using a button. Where can I set it?