I worked on your issue here. Here is what i tried : I manually entered the exposure as 2.10, then as 2.20 and 2.30. Then undo the 2.30 (using the keyboard shortcut), it takes the exposure down to 2.20 and then again to 2.10.
I was unable to reproduce it. Is there any step i am missing ? Could you please elaborate it with a video ?
I assume from your recent post that you are using Lr Classic 8.0. Can you send your system configuration here as well ?