Then I confused it with another strange XT/AT clone. I see, this mouse seems to be even Amiga compatible!https://www.seasip.info/AmstradXT/1512tech/section1.html
Did it type random characters in DOS text mode due to connection to the keyboard port? (C64 does such things when moving the joystick.) I also remember in shopping centers there was an XT/AT (pc1512?) that had a B/W monitor with long persistence "white" phosphor, but new appearing letters or flashing cursor started glowing pink, and the afterglow was green or such - very odd behaviour.