I recently upgraded from PVST to MST, and at some point inter-VLAN routing got broken. I can't say for sure that the MST upgrade was the cause, but it happened during the same period.
Here is what I have determined:
My management VLAN is VLAN2.
The layer 3 switch can ping a device in VLAN5 on a connected switch, so I don't suspect trunking misconfiguration.
The connected switch is unable to ping the device in VLAN5. When a traceroute is run, it dies in 1 hop on the L3 switch at the management VLAN interface (10.8.2.1).
All switches can ping each other, and all non L3 switches are able to ping all VLAN interfaces.
This seems like such a simple problem, yet for the life of me I don't know what's going on. IP routing is enabled on my L3 device.