Re-Opening the app resets classes.txt

I have a folder with (let'a say) 1000 images. About 200 of them was already processed with labelImg to label "tag" and "mini-tag". I close the app, classes.txt have the tag and mini-tag at the end nicely. The next day I open up the folder with "Open Dir", it recognises yesterday's work. When I want to add a new class "like weapon", I add the RectBox, add the class weapon ( At this time, strangely the list doesn't contain tag and mini-tag already ), save my job and what happens? Classes.txt gets erased, and now it looks like the default classes.txt + the class "weapon". tag and mini-tag have disappeared. Every time when I re-open the application I have to add random RectBoxes with the name of the previous classes, save it, then I can only continue my work.

Why does the app resets the classes.txt and does not read it properly when I open the folder containing it?