Lost contains (about 1kb, 1024 bytes length) randomly in EOF

[TonoYuki]

SYSTEM: Microsoft Windows 10 Professional [10.0.19045.6093]

When I open and edited some long files (128kb or longer), and save, the contains sometimes will lost (from EOF, and backwards about 1024 bytes length), or sometimes normally saved, without any lost.

I wonder how and why the contains near the EOF could be lost randomly?

[lhecker]

Maybe I have a bug somewhere. Do you have a file that reproduces the issue? If so, could you send it to me (privately)?

[TonoYuki]

test_GB18030.txt

Here, take this. (The whole file contains "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789[CR][LF]" FULL-WIDTH characters of GB18030 code page, and it repeated 4096 times)

Here is the deal: when you add a [CR][LF] in the EOF, and enter some random characters in the line which was created by the new [CR][LF], and save, the previous contains of text will disappear (random length, not strictly 1024 bytes, but less than the whole file); then you keep these changes just now with your edit.exe running (DO NOT CLOSE), and enter some random characters in the line which was already existed (after these "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"), and save, the previous contains of text which was disappeared could appear again.

I thought that was an obviously bug of some East-Asian code pages (due to the full-width characters in ANSI).