It looks like it tokenizes right, at least on my local install and meta.
[5] pry(main)> Post.exec_sql("SELECT * FROM ts_debug('english', 'wb.camra.org.uk');").to_a
=> [{"alias"=>"host",
"description"=>"Host",
"token"=>"wb.camra.org.uk",
"dictionaries"=>"{simple}",
"dictionary"=>"simple",
"lexemes"=>"{wb.camra.org.uk}"}]
So this is likely an implementation bug on our side.