The Broken Switch Port Issue is raised when the following two conditions are met:

Value of dot1dStpPortState equals ‘broken’ && The Status of the port is up

A little more detail on the dot1dStpPortState mib

Values:

1 : disabled
2 : blocking
3 : listening
4 : learning
5 : forwarding
6 : broken

Description:

"The port's current state, as defined by application of
the Spanning Tree Protocol. This state controls what
action a port takes on reception of a frame. If the
bridge has detected a port that is malfunctioning, it
will place that port into the broken(6) state. For
ports that are disabled (see dot1dStpPortEnable), this
object will have a value of disabled(1)."