A very problematic issue, that I see now again, while posting here (I have seen it on another site, but thought, the issue was introduced by that site), is when editing a text.
I start writing a text in some kind of edit box (writing this post, or chatting on faceobok.com), then, when I move the cursor back, and trying to insert a text in the middle, some letters are eaten. I have checked, that 'Insert' function is turned off. At faceobok.com, the cursor returns to the end of the text.
When I press MMB back in that place, the problem vanishes temporarily.