When I try to build it automatically mines a large area without me clicking anything.

I have had the issue in 1.15.2 and it just mines one block automatically without me clicking as it was so few blocks I turned my mouse sensitivity down to 85% but when I tried it on 20w20b with the mouse sensitivity on 85% still it was much much worse and mined a large area automatically mining for around 5 seconds before stopping it would move around as it did it 

I expected it to just let me build and mine when I click the corresponding button 

what actually happened is when I let go of the button it began to mine automatically

To recreate it in 1.15.2 

you need to just play the game as usual and a t random points it will mine a block without you having to click anything.

To recreate it in 20w20b

you need to start building I was trying to build a house with cobblestone. you should have the mine and build controls on default then you should just let go and see that it mines without anything being pressed.