I just noticed. Whether this is really a bug ... I doubt it myself.
(i like the feature that you can expand your redstone panels 👍 )

But I noticed it anyway :)

If you place two panels it looks like this

if i remove the second panel

=============

if i place only one panel:

after placing a second panel:

Ah. Pistons are only being notified of neighbor block redstone updates, not neighbor block changes affecting extendability.