Apparently nothing gets comments going like boring programming stuff. 
Anyways, the exciting conclusion!
You were all wrong. I was wrong. Well, half-wrong After all, the buggy code did rise from the grave and came back to haunt me one month later! Just in time for Halloween.
The _speed variable in question was inherited from MovingTarget. Which would’ve been fine, except there was a leftover _speed variable in Craft too. Uninitialized too, naturally. Just hiding there, no warnings, no anything, just happily confusing me and the compiler. Ain’t programming wonderful? A learning experience every day.
Haha, I at least like to think I was on the right track after mentioning inheritance
In any case, it’s good to hear that you tracked the error down!
Congratulation to solve this thing!
More posts like this would be great!
Whole OpenXCom is really interesting.