Random channel offsets

Hello everyone,
I get this really weird bug with a standalone plugin under Linux: the output channels I write to are always the same (e.g. 0 to 8), but the outputs on the audio device (MOTU UltraLite AVB) keep randomly changing (they are still contiguous, but with a wrap-around).
Is this a known problem? Is it rather related to the OS or to JUCE?
Best regards,
Fritz