"preproc.substitute_unicode=false" works properly only if sketch is not saved

Hi, dear!
Setting "preproc.substitute_unicode=false" works properly only if sketch is not saved.
If sketch is saved, some functions, such as "lcd.print(String)", still send a unicode (two bytes char) to display.
If sketch is not saved (any change, like one more space in comment string) - it's all right.
PS. I'm using Cyrillic codepage 1251
PPS. Arduino IDE 1.8.5 (and older)

Reproduce the issue in Arduino IDE 1.x with preproc.substitute_unicode=false, comparing a saved sketch with an unsaved sketch and lcd.print(String) using Cyrillic codepage 1251. Trace the preprocessing path and identify why saved sketches differ; done means Unicode substitution is consistently disabled in both states.

Written by the indexing model from the issue text.