It's a bug in the OB6's MPE code. As you step through midi channels to the 17th slot to select MPE, the synth gets confused and thinks it's using midi channel 17. If you send pitchbend on ch 17 it is actually sysex! They have the same bug for program changes which again are on Ch 17 and are received as aftertouch! I told Sequential about this in April... My Low Frequency Expander has to unpick these garbage messages and correct them. Program changes are always preceded by bank changes so if I receive a bank change followed by aftertouch I know it's actually a program change and if I receive a garbage sysex start with a particular fingerprint I know it's meant to be pitch bend. PITA but works perfectly when unpicked and corrected!