Regarding the “Bug Fixes : Fixed a bug where double-clicking a word might not select the correct word when the CSV selection mode is disabled.”
EE v17.5.0 will select the correct word in the Cell when the Cell selection mode is disabled or enabled.
But there are some different behavior in the Cell toolbar:
Example 1.
Double-clicking “test” in the Cell toolbar, it will select the “test” and the space ” ” between “test” and “abcd”.

(If Double-clicking “test” in the Cell, it will select the correct word “test” only.)
Example 2.
Step a. Double-clicking “test” in the Cell toolbar,
Step b. Wait a second, and then click on the “test”.
This step should cancel the selection, but actually not.
Step c. Move the mouse cursor, it seems the mouse left button still pressed, so the Selection color will also move accordingly.
But actually it did not pressed the mouse left button.

(If step b, click on the rear of “test” or outside of Cell toolbar, this situation will not happen, it will cancel the selection correctly.
And this situation start from v17.1.2, I am not sure if it is behavior change or bug ? )