I've been attempting to create a custom movement similar to the Mushrooms in Super Mario Bros, and this has all worked out fine. However, if I add more than one mushroom object on screen at the same time, everything messes up. (If I remember correctly, the first NES game only allowed one Mushroom on screen anyway, but not the games after!)
I've posted the file on the ClickTeam forums, but am posting here too in hope of a responce.
The problem is that you're using fast loops. In order for them to work with multiply copies of the same object you need to have some kind of nested loop system where each loop is run for each object individually. I don't have time at the moment, but later I might try and see if I can fix it.