[Urgent] Command block UI is glitching and unexpectedly altering commands

Verification builds: 1.2 (464771)
Summary:
When editing a command on a Command Block, the "+" (expand) button in the Command Block UI is glitching, sometimes the original command is lost if you do not press "Cancel".

Impact:
When a command is typed, if you decide to jump into the 'full screen' command editor, your previously typed command is lost. Sometimes, the UI is populated with an old command, potentially from a different command block.

Repro Steps:

1. Place down a command block
2. Type `/say Test 1` and then hit the `+` button
3. In the full screen editor, append additional text and press ESC
4. The command will no longer be correct. If you edit several different Command Blocks, sometimes the UI also populates itself with commands from other Command Blocks.

Observed Results:
The command displayed in either editor is invalid.

Expected Results:
When switching between the inline and full command editor, the results should be consistent. Command Blocks should not be populated with commands from other blocks; we've experienced this several times and as a result, it has messed up some logic when reading existing command blocks.

Screenshots/Videos attached: Yes (https://youtu.be/3yvPK0D8THA)

Notes: