Why do i observe a change of Midi channel from 0 to 1 with VST3 on linux?

i wrote two VST3 plugins with JUCE v7.0.5 and use them in series with Juce HOST.
Plugin 1: midi → midi
Plugin 2 : midi → audio is a synthesizer

Curiously when Plugin 1 sends “note on” on channel 0 then Plugin 2 receives the note on channel 1, as i if Juce or the host changes the channel number?
( But no similar problem for channels 1 to 15.)
Why is it so?

JUCE uses indices 1-16 not 0-15 as programers might expect to refer to the midi channels. So a channel index of 0 is invalid in JUCE. Might this be the cause for the confusion?

Thanks very much, this was indeed my mistake.