Description of the Issue

When I create and save a text file containing only the text "Хз." (in Russian), which has Windows string ending and UTF-8 w\o BOM encoding, it transforms to TIS-620 encoding, and containing text becomes "ะฅะท." Seems to not happen with longer texts inside files. Also doesn't happen if you change "Хз" to some other two letters, for ex. "Чо", "Иа", "Ха" (in Russian).
Checked on versions 7.3.3 (32bit) and 7.4.2 (64bit).
Plugins disabling makes no effect.
OS is Windows 7 64-bit.

Steps to Reproduce the Issue

1. Create a file with Windows string ending and UTF-8 w\o BOM encoding
2. Write "Хз." in it (in Russian)
3. Save and close
4. Reopen this file

Debug info

Notepad++ v7.4.2 (64-bit)
Build time : Jun 18 2017 - 23:38:43
Path : D:\Program Files\Notepad++\notepad++.exe
Admin mode : ON
Local Conf mode : OFF
OS : Windows 7 (64-bit)
Plugins : mimeTools.dll NppConverter.dll