libpq: COPY FROM STDIN BINARY of arrays

Hi,

I already use arrays fine (e.g. text[]) in BINARY mode binds (with prepared
statement or not).
I already use COPY FROM STDIN BINARY fine, with scalar values.

But for the 1st time, I'm combining COPY with arrays,
and it is NOT fine yet :(

#08P01: ERROR: insufficient data left in message
CONTEXT: COPY UT_LibPQ_copy_arrays, line 1, column ptys

Does the wire-format of arrays differ between binary-binds and binary-copy?
Any pointers to what I could look at, to resolve this? doc? code? example?

Thanks, --DD

PS: If that helps, I'm willing to detail the break-down of all values /
bytes I'm sending