With both BetaFeatures enabled, in 2017WE mode, there's a strange bug if I follow this sequence:

• Start with cursor on newline
• Type [space] and [any character]
• go to end of line above
• press [delete]

The space and character on the original line will still be visible (as well as being moved up, to the line above, as expected). (See video)

Additionally, if I try to alter the original line's space+character, will lead to unpredictable behavior:

• If I try to use keyboard arrows to move the cursor there, I cannot.
• If I use my mouse to move the cursor there, it works, but anything I type will not be saved, and will scroll off the bottom of the edit-area. (See screenshot)

Nothing useful in webconsole.