HTTP 431 error response to PDB query if too many structures

Fetch ENST00000251595 (haemoglobin) from Ensembl, select ENST00000251595, show Uniprot cross-references.
Peptide has 260 PDB cross-references.
Right-click | 3D Structure Data... the list appears.
Customise displayed options and add a column.
Now get an error (blank message) when displaying results, either immediately or after switching to 'Most Protein Chain'.