I have two 3750’s configured as a single stack. I am doing some testing now and I have a single 2921 router connected to switch1. I have interface Gig0/0 configured as a /30 and Gig 0/1 as a / 30 on a different subnet. I converted the two ports on the 3750 to layer 3 ports and given them the other IP on the /30 network. I have VLAN 1 on the 3750 acting as the default gateway which is the gateway that my PC is using. On the 3750 and the 2921 I am using EIGRP to exchange routes. I have a loopback interface on the 2921 to test connectivity. When I do a show IP route on the 3750 that is my gateway I see two routes in the routing table for the loopback interface going over both of the 2921 interfaces. I then setup a ping between my PC and the loopback interface. When I shutdown one of the interfaces on the 3750 I loose between 1 and 2 ping packets. I would have thought that with the load balancing in place the second route remains and I would not loose any packets.
I have this problem too.