uc_fee.js: String.prototype.bytes

String.prototype.bytes is defined differently than in uc_taxes. This causes issues with uc_taxes when uc_fee is called after.
uc_fee:

String.prototype.bytes = function() {
    return Drupal.encodeURIComponent(this).replace(/%../g, 'x').length;
};

uc_taxes:

String.prototype.bytes = function() {
  // Drupal.encodeURIComponent() gets around some weirdness in
  // encodeURIComponent(), but encodes some characters twice. The first
  // replace takes care of those while the second lets String.length count
  // the multi-byte characters.
  return Drupal.encodeURIComponent(this).replace(/%252[36F]/g, 'x').replace(/%../g, 'x').length;
};

Suggestion: instead of overloading a primitive data type, define a custom function - str2bytes(str)