After examining this bug closely I'm afraid the fix is rather
serious. What I will do is change the system such that all
interaction (except for attacks) is disallowed after a unit begins
movement. This means no more stacking with or giving items to a
unit on the same day it begins moving.
I looked at implementing ways to try to patch up the travel time
after the move had begun, but there are other loopholes with this
bug approach and I fear I may not spot them all and that the only
comprehensive solution is simply to consider a unit to have left
after it has issued a MOVE order.
Other side-effects are that units which have issued MOVE will not
auto-attack or participate in battles on the first morning of their
MOVE, as they have done in the past.
There may be other unforseen effects this change has, which have
not occured to me.