erased brocade 6450 causing problems on network it came from

[ruckus-paul]

We are currently replacing our old brocade ICX network switches (6450s ) and replacing with Ruckus 7150s. We have all but one stack of switches replaced.  We thought maybe we could re-use our old switches as isoloated or unmanaged switches but after we wiped the 6450s, and restarted them, checked the running config and nothing is listed in running config, when we plug the switch into the network it causes problems with at least one one of our servers and it will be unreachable, as soon as we unplug it it comes right back (pinging from another computer hooked up to a different switch).  For our use, we would just like to use it as a layer 2 switch but don't know how to turn off or disable the layer 3.  (we are connecting the erased switch via rj45 into a layer 2 switch)  is there something that we are forgetting to do or need to do to get this working?