Selecting work rosters: selections clearing themselves/adding to roster

I'm attempting to get a nice work roster set for my janitors. It seems I can select different rides and shops with the multi select too, but if I hold Cntrl and then click to remove something (like a coaster track), all the items I selected disappear (become un-highlighted). If I hold the 1st or 2nd button down in the multi-select corner I can add rides and shops, but it seems eventually everything will clear out when I select something. In other words, I get to the end of selecting everything, then all my work is gone. It seems very random.

Also, holding down Ctrl and Shift while using those buttons gets the same results, which doesn't make a lot of sense to me. I've tried this many times and keep giving up... I did have it work once, but it was in a non-crowded area of the park; a small midway.
You've probably clicked something else than a ride/shop/facility. Happens to me all the times, when you are in building mode and click something that is not part of that building it deselects all as well.
^It's a bit confusing; how do you select many items with out the whole thing being "undone" by accident? I've done the multi-select "box" method, and then will Cntrl to remove one item, the whole thing disappears again.

Also, it seems if I click a hot dog shop, it's all good... but if I click a hot dog shop that I built myself, it deselects everything. I could swear it was all random. Is there a good video that explains this and the what to do/what not to do's?