Loading a file larger than 5.242.880 bytes insert newline in QPlainTextEdit

Below is a project I use to load a large file. But when the file exceeds 5,242,880 bytes, an extra new line is inserted. So character 5.242.881 is inserted on the next line.

I’ve created a text file with 32767 lines of exactly 160 bytes (including 2 bytes for \r\n, thus 158 characters + \r\n).
Line 32768 has exactly 80 characters. This file load fine.

When I add 1 character to line 32768, this character will be displayed on a new line. Obviously not correct.