External keyboard navigation bug
There is a bug in arrow key handling that causes the insertion point to jump to the end of document when up or down arrow is pressed on an external keyboard in certain circumstances. Perhaps it’s interpreting the arrow as Cmd+arrow (“move to end”). I’ve got a screen recording of the issue if anyone would like to see it.
Just to bump this... I have a similar problem in Pythonista, except that my up/down arrow keys don't move from line to line at all unless I hold down shift (in which case, it selects the line of text between cursor positions). There is nothing wrong with the keyboard as I use it daily (e.g. to write this comment).
Other key combinations don't make sense, either. For example, option+down goes down two lines, while option+up goes up one line. Command+down jumps to the end of the document, but command+up seems to do nothing. Control+down and control+up seems to jump to the beginning and end of the document correctly.
The IDE is pretty tough to use in it's current state, unforunately. :/