Hi,
I’m sorry if this has been brought up before (I tried search but could not find any). I would be surprised if this has not been brought up before! Also, I’m not sure if this qualifies as a bug report, hence I post this here.
In short: Moving the mouse should not move / change the option chosen by the keyboard.
Currently, if I choose something with cursor keys, move the mouse (but not click on anything!) and press enter, whatever which was under the mouse will be chosen and entered (instead where I had navigated with my mouse). This breaks common UI rules: Usually there is a separate keyboard cursor – movable e.g. with TAB, or sometimes with cursor keys. The mouse does nothing to this cursor – unless clicked (which usually also moves the keyboard “cursor” focus)!
This is actually a problem, since my mouse is quite sensitive (and the table it is on, is also sensitive and shakes a bit when I type). Sometimes (which is quite often) something totally different is selected which I intended!
Solution1: Move keyboard elsewhere. I actually use it from my lap because of this, although I’d prefer the table. Which is a bit cumbersome 
Solution2: Unplug the mouse. But this is cubersome, even although one does not use mouse in KODI, one might be using KODI on a desktop interface with other software open at the same time…
Solution3: Disable mouse in KODI. But as it is sometimes handy to have the mouse in addition to keyboard enabled, this is not a fix (but a workaround).
Solution4: Fix this code-wise. But it might not be easy (I’m not a programmer, and haven’t looked at the code, but there might be reasons it works the way it does currently; perhaps because of touch interface code, or highlighting of the menu or something…)