If a plan's trigger is a separation from service, and it currently provides that any benefit will be paid in a single lump sum payment within 90 days after separation from service, why would it include the following provision: "with respect to Participants who Separate between December 15 and December 31 of a year, payment will be made on or before March 15 of the following calendar year." I cannot think of a reason for including this provision in the Plan, as I do not believe the payment will qualify as a short term deferral under 409A for prior year deferrals.
Any thoughts?

This is just off the top of my head, but I believe that the Regulations do not allow the designated window during which distributions will be made to straddle two different tax years, but they do permit payments to be made later than the date specified, as long as payment is made by the later of 1) the end of the tax year in which the participant becomes entitled to payment or 2) 2 1/2 months following the date he/she becomes entitled to payment. I think the prohibition on having the payment window straddle two tax years may only apply when that window is objectively determinable at the time the agreement is entered into (i.e. if the agreement provides that the participant will Separate from Service on Dec. 20, and that payment will be made w/in 90 days of S/S), so that particular provision may not be necessary in the agreement if the date of termination is not known at the time the agreement is entered into.