Editor displays file content incorrectly after external file saving and autoload after prompt

I faced editor issues when editing same sql file in HeidiSQL and external editor (Notepad++). Somehow if file contains zero char inside the text, HeidiSQL editor saves only the part until this zero char. Though in window the content was displayed full up until file end. So I lost significant part of my work. Then I noticed that my file becomes bigger size than it was. I found that special characters in UTF-8 file are displayed wrong (as two symbols instead of one) after file load by HeidiSQL after outside file save detected. On subsequent parallel save operations my file from 4 MB increased its' size up to 300 MB. And the problem is on HeidiSQL editor side, because of the following test. After special character scum, displayed in editor I close the file without saving. Then I open new query tab, right click and "Load SQL file...". I select same file. And it is loaded and displayed correctly with one symbol displayed for two bytes in file for that symbol. Reproduced with 11.3.0.6392 (64 bit).