Most recent kernel where this bug did not occur: 2.6.17-10
Distribution: Ubuntu, Fedora, Dynebolic, Gentoo
Hardware Environment: IBM Thinkpad T42, desktop with Ensoniq AudioPCI ES1371, MOTU Fastlane USB midi interface
Software Environment: awmidi, rosegarden
Problem Description:
A midi interface is recognized by the system.  awmidi(1), rosegarden(1) and other midi-using programs report its presence, but cannot receive or send data through it.  

Steps to reproduce:
1) Hook up a MIDI keyboard to the joystick/MIDI port or a USB MIDI adapter such as a MOTU Fastlane.  This particular USB MIDI adapter does not require its firmware to be uploaded when it's plugged in.

2)
$ amidi -l
Dir Device    Name
IO  hw:0,0    ES1371
IO hw:1,0,0  Fastlane MIDI A
IO hw:1,0,1  Fastlane MIDI B

This shows available MIDI ports.  ES1371 appears on the joystick port.  Curiously, with kernels 2.6.17 and prior, the "Dir" column is missing.

3)
$ amidi -d -p hw:1,0,0

Now press some keys on the MIDI keyboard.  If the kernel is 2.6.18 or higher, nothing will be output.  If the kernel is 2.6.17 or earlier, hex numbers will be printed for each keypress.