Connecting 3 switches to a fourth switch, each with its own crossover cable shuts down ports

This is probably a very basic question but I need to ask it anyway since there is no easy way to test it while everyone is on the network. I have (3) 3com switches, all are connected via a proprietary backplane cable called a matrix cable whis is sort of like a crossover cable. I added a fourth switch, a Cisco catalyst, and decided to plug each 3com into the Cisco switch using three crossover cables, one cable for each 3com, connected to the Cisco. Later I would connect the Cisco to a trunk. After plugging in the three xover cables I noticed only one port was active, and if I unplugged the active port, one of the other two ports became active. Is this spannig tree? was it doing this to prevent a loop? Will this config work once I remove the matrix/ backplane cable?

thanks NH