Currently, the Tokenizer just drops data bytes if there was no status byte set in the current message:

The MIDI spec, however, allows to omit status bytes (see MIDI running status) in which case the last transmitted status should be used. In my case a hardware device uses this feature and by this totally scrambles the parser state. 😢

If I see this correctly, the only change needed would be to store the last status byte when completing a message with at least one data byte and only ignore 'stray data bytes' if nothing was set yet.