"Back Space" and Selection fail to change correctly units (mm/in) in Page Settings

3.0.2 / Windows7

1) Default score
2) Page Settings
3) Scaling: place the cursor after the "4"
4) "Back Space" twice
5) Retype eg "20"

Result: nothing happens

Same bad result with selection: eg highlight the "64", and retype "20". New failure.
Or with same selection: remove, and type "20"

Result: only the "2" is entered.

So, something turned wrong here (maybe elsewehere too?)

• I see a change (the breakage) in January, 2017. More details soon.

• See the comparison (first screen with 2.3.2, second screen with 3.0.2)