We had this happen in the UAL/CAL merger. The day before the SLI result was announced a vacancy bid with about 250 Captain slots for only CAL pilots went out, since CAL management was running the airline and they wanted to ensure their pilots grabbed as many slots as possible. They were for training in as much as a year in advance. Then right before the fence fell for the 747/787 management put out a massive 150+ pilot bid only for 787 (so only CAL pilots could bid it) and they again locked up the next year of slots. It ended up that the junior 787 Captain went to almost 30% on the overall list, which unheard of for WB Captain.

I suspect that this could be something like that. No reason to do this right before every pilot can use their seniority to bid, especially when its this obvious.