This could make a little more sense with a Composite. You almost have to be picking CS to initiate a normal slowdown but unlike a WCR, CS does not directly initiate a door open. In this case UC, CC, DC call transfer contacts pick CS and and they also pick CR which picks CST. CST initiated an auto open. So anything that caused CS to pick but not CR like a crossed up or shorted contact on N/O UC, DC, CC, or V in the CS coil circuit. Just to give you somewhere to start.