Since the "rule" was never clearly specified I'm not sure how you came to the conclusion that this is indeed a "bug". Can you point me to the rule please?
With your logic this whole game is a "bug". LOL.
In order for the whole game to be a bug, it would have to not follow its rulebook completely. While there have been and are discrepencies, the vast bulk of the rules are implemented correctly.
Anyhow, it's a negative inference: There is nothing in the rules that state or imply that having your corps loaned to another power will cause your corps to no longer be at war with your current enemy. Since it IS still YOUR corps, and your power IS still at war, the battle should be allowed.
In order for corps loaning to be considered to remove the corps from the war, it would have to overtly state that, as it does for supply purposes and other considerations.
There is nothing in the rulebook that states or implies that the loaned corps is still under your command, which by action (observation) it is not, therefore it's entirely possible to derive a reasonable conclusion that the corps no longer, temporarily, belongs to you and is therefore not subject to the same situation.
I agree that this makes no sense but it doesn't change the rules.
Also, since there is nothing in the rulebook stating otherwise then it's reasonable to consider this not a bug and, in fact, the implementation of the rules since there is NOTHING in the rulebook that contradicts this in anyway, shape or form.
So if there is a way like there was in version 1.00 to "get free factors" just by doing some tricky factor transfers it would be ok, since its not in the manual it can not be a bug.. ?
I believe that the manual covers how to get factors, so no, that would be a bug.
I'm done arguing about this it's just a waste of time. Think what you want I don't care.