Hello Peter,
why "it is expected"?
In my case I need to have 2 taxonomic fields for 2 different purposes in WooCommerce "product_cat" taxonomy.
Why shouldn't it be possible to have 2 taxonomy fields with same configuration for the taxonomy attribute ('taxonomy' => 'product_cat')?
Why can I use 2 text fields, but not 2 taxonomy!?
Can you fix it?

Thank you
Alessandro