Multi Select & Select Fields Reloading Suitelet

I have a suitelet that creates a form which includes a multi select field (from a custom record) and a regular select field (dropdown customlist)..

When the user selects the list (from the sublist dropdown) or the multiselect button the suitelet appears to RELOAD and all my declared variables disappear.

The following is a snippet of the code for setting up the fields on the form:

var form = nlapiCreateForm(SUITELET_TITLE, true);

var fldCustomer = form.addField('custpagecustomer', 'select', 'Customer', 'customer');
fldCustomer.setDisplayType('disabled');
fldCustomer.setDefaultValue(stCustomerName);

var fldPONumb = form.addField('custpage_ponumb', 'text', 'PO Number');
fldPONumb.setDisplayType('disabled');
fldPONumb.setDefaultValue(stPONumb);