On Android 4.4 using Chrome beta 60.0.3112 or Opera Mini 28.0.2254, I access a mobile Wikipedia page such as https://en.m.wikipedia.org/wiki/Hanoi as a logged-out user. I start to edit the page, scroll two screenfuls down, and delete a character with backspace. At this point the viewing window jumps up about a screenful, so that the cursor is not visible anymore. If I then enter a character, the viewing window jumps back to the cursor, and the character is properly inserted.
My phone's screen is rather small (Samsung Galaxy S2) and while editing it shows only 9 lines of text above the keyboard. I believe this is part of the problem. The jumping-while-editing can also be observed when editing a mobile Wikipedia page with a desktop browser, but there it doesn't cause problems since there is no keyboard obscuring screen real estate.