Textarea buggy on Android?

Question

Android

There is a problem with text selection, it seems to be inverted and by pressing Backspace, not what is selected, but part of the text above is deleted. Clearly: https://youtu.be/2rfwzjsf6DI
In addition, I have a Swift keyboard installed and writing HTML tags on it is not realistic at all, but this problem does not exist on the standard one. I suspect it's autocorrect or something.
The point is that there are no such problems in other textarea. That is, the problem is either in the iframe in which my textarea is located, or in some settings that I did not make.
What to do with textarea? Or maybe there are alternative textboxes? Like, I read somewhere about a text div.