All conversions will use the Original_format if it exists
This is so you don't stack fail onto fail.
OTOH if you fix things in the converted EPUB, but do another conversion, you will lose those because the Original will be used as the conversion source.
You are
if you don't learn (and use) HTML + CSS
There is NO magic bullet fix just as there is no single way to get text placed (although, some are really nasty lookin code)
And sometimes you are fighting the device, not bad/sloppy code.
KEPB will run words together if the CSS for that style has set
letter-spacing (It seems it 0's the space character).
Just because the code is Valid, does not mean it will work on all devices.