Error when putting existing fields under new fieldset

If I want to create a new fieldset and put some fields under it, I receive an error.

What to do to recreate this error
1) Add some fields to the webform
2) Fill in the details for a new fieldset (don't add it)
3) Drag the existing fields underneath it
4) Press 'Save' down the bottom
5) Receive error.

General error: 1366 Incorrect integer value: '' for column 'pid' at row 1: UPDATE {webform_component} SET pid=:db_update_placeholder_0, form_key=:db_update_placeholder_1, name=:db_update_placeholder_2, type=:db_update_placeholder_3, value=:db_update_placeholder_4, extra=:db_update_placeholder_5, mandatory=:db_update_placeholder_6, weight=:db_update_placeholder_7 WHERE (nid = :db_condition_placeholder_0) AND (cid = :db_condition_placeholder_1) ; Array ( [:db_update_placeholder_0] => [:db_update_placeholder_1] => first_name [:db_update_placeholder_2] => First Name [:db_update_placeholder_3] => textfield [:db_update_placeholder_4] => [:db_update_placeholder_5] => a:13:{s:13:"title_display";s:6:"before";s:7:"private";i:0;s:8:"disabled";i:0;s:6:"unique";i:0;s:20:"conditional_operator";s:1:"=";s:5:"width";s:0:"";s:9:"maxlength";s:0:"";s:12:"field_prefix";s:0:"";s:12:"field_suffix";s:0:"";s:11:"description";s:0:"";s:10:"attributes";a:0:{}s:21:"conditional_component";s:0:"";s:18:"conditional_values";s:0:"";} [:db_update_placeholder_6] => 1 [:db_update_placeholder_7] => 11 [:db_condition_placeholder_0] => 24 [:db_condition_placeholder_1] => 1 ) in webform_component_update()

Hope I've been clear enough, it's not a big problem at all, I may even have a look at the code myself and see if I can come up with a fix.

Cheers