Slicer maintain choices

I have a report where I keep several items pre selected on a slicer. I cannot use the report level filter because, for some reason, it arbitrarily selects a percentage of items to list. The problem isn't that a slicer must be used, I really don't mind the slicer. The problem is, when adding new selections it randomly clears a portion of those who were already selected. This is a list of our vendors (around 281 total) and we highlight about 25 - 30 to monitor. If I add five more, the slicer will go from having 30 selected to having about 22 selected plus the one I just clicked. There is no rhyme or reason and it is never the same ones dropped. It is very frustrating to have to go back through the entire list to find what was dropped and add new ones. Any suggestions?
Can slicers please maintain all selections when adding new ones?