I don't doubt that disabling the mouse will activate the keys. But that doesn't prove it's impossible to use them at the same time by the game's design.
For all I know its some obscure memory emulation problem or an irq or something preventing the keyboard from fully loading while the mouse is in memory.
It seems very strange to me that the designers would go out of their way to disable the keyboard during mouse play. Not saying it's impossible, just hard to believe. I could see it being done to preserve memory, but you'd think it would be mentioned in the manual or the setup menu or something.
The manual warns of nothing like that. It does however say "The keyboard commands may not be available on all systems, refer to your Data Card for details"
http://www.lemonamiga.com/games/docs.php?id=584 This is apparently that Data Card. Which also fails to mention this either or situation.
Do you have any kind of citation that this is in fact the case? Again, not that I don't believe you, it's just that this is a deal breaker for me, and if I'm going to quit I would rather not do it based only on your word heh.