$wpdb->insert() inserts duplicate rows (against my wishes)

Question

I am trying to do a more or less routine insert however my code appears to be being called twice. Here is said code:

$market_arr = array(
    'market_name' => $market,
    'future_market_code' => $future_code,
    'fx_market_code' => $fx_code,
    'cfd_market_code' => $cfd_code,
    'etf_market_code' => $etf_code,
    'option_market_code' => $option
);
$wpdb->insert('bu_trade_market', $market_arr);
$market_id = $wpdb->get_var($wpdb->prepare("SELECT market_id FROM bu_trade_market ORDER BY market_id DESC LIMIT 1"));

As it may have a bearing:

• The code is in a plugin file
• The code is being called by the page via a function courtesy of exec-php
  • Function literally consists of require('page-in-question.php');
• I have tried disabling all plugins save my custom plugin and exec-php
• I have tried adding $wpdb->flush() to the end of the page
• It inserts once if I put exit; at the base of the file but fails to load the template.

I am EXTREMELY hesitant to make a custom template file for this as it would mean I will need ~100 custom template files.

My question essentially is this: How do I stop it from executing twice.