If slots are for a route assigned to an aircraft that is near delivery (say within a week or so - perhaps?), allow the airline to retain the slots until then.
I received the confounding Slot Warning message again, telling me to "please schedule aircraft to these routes immediately". When clicking the links through to the routes, I found that they are already assigned to an aircraft. Similar to what I ran into here...http://www.airwaysim.com/forum/index.php/topic,47624.0.html
As it turns out, that aircraft was a new order from the factory within days of delivery. I did happen to have an alternate aircraft available, so moved the routes to that aircraft and no more message. Those routes were from an aircraft lease I purposefully terminated with the new factory order as the replacement. I have limited ability to affect the timing of either action.
Would be nice if the algorithm is smart enough to "know" that the slot is assigned to an aircraft about to be delivered and allow that as an exception.
Perhaps an original target date for slot expiration and a max variance from this for routes assigned to aircraft to be delivered are both tracked such that no one can game this with repetitive assignments. I also suggest that this applies to new factory aircraft vs used aircraft (that are easier to align timing on).