There have been an increase in the number of people reporting recently that reservations are being merged without being requested. Meanwhile some people are waiting days for reservations to be merged at their request.
Many members do this so they can look to switch one or both at 7 months. One of the DIS mods emaile Member Services and has been told it shouldn’t be happening and they will pass it on to mgt.
But to be safe, if you do book 2 or more reservations for the same room type & category and do not want them merged, make sure you add an extra guest to one of them, or use a different name for the lead guest. They cannot then be merged.
It would probably also be useful if more people emailed Member Services about it.