Summary
Prior to the 1.14 update, if a long command string was placed in a command block, you could easily use Shift (+ Ctrl) + L/R Arrow to select a part of the command in the command line and the command would scroll with the selection if the selection went out of view. However, after 1.14, this no longer works. Tested in 1.16.2, the problem still persists.
Example
I have a string that lists numbers 1 - 27 typed into a command block. I place my cursor before the number 1, then use Shift + Right Arrow to select forward.
Prior to 1.14:
[media]The command line scrolls to reveal what is being selected. The number 27 is visible.
1.14 to Present:
[media]The command line does not scroll to reveal what is being selected. The number 27 is selected but is off-screen.
This is only an example and I realize that Ctrl + A selects the entire string. This problem specifically hinders the selection of a segment of code, not the entire line.
Reason
Some may think this isn't much of a problem because mapmakers and coders should be using functions or some other method of typing long commands, but that isn't an excuse to make something less intuitive. What about beginners? Or people who do not prefer to switch over from command blocks? Or even those, like myself, who need this functionality for testing a specific line of code before implementing it in a function? It's very minor, but it's definitely infuriating.
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Was able to replicate a similar issue where it wouldn't scroll on to the rest of the command in Minecraft windows ten edition 1.16.10. (Also replicated in windows 10 environment on 1.16.2 in java).