while replacing the brake pads tonight, i noticed an odd occurence. doing the drivers side, i didnt have a problem and the rotor had no gouges and felt nice and snug. however, after taking the caliper off the passenger side the rotor felt loose and slipped right off. the bearing on the wheel and the hub felt solid as a rock though and had no play. this must be a really stupid question [you can tell me if it is] but is the rotor supposed to just slide off like that? maybe i jarred it loose when wiggling off the caliper but i thought it had a key or groove that locked it into place. obviously, its fine once you put the caliper and the tire lugs back on, i just was curious if this was normal or not.