'To' year changes to current 'year' when editing node

Drupal 6.8
MySQL 5.0.51a
PHP 5.2.8
Date 6.x-2.x-dev 2008/12/18

Not sure if this is a bug or something I am missing so I have marked the issue as Support Request.

I am using a CCK_Date field in an historical date context with a granularity of 'year'. When I open a node in Edit mode the historical dates eg.:

Date FROM = 1821, Date TO = 1911 are correct,

on saving the node, the 'FROM' date retains the correct value but the 'TO' date resets to the current year e.g.:

Date FROM = 1821, Date TO = 2008.

Tried this on several nodes with differing ranges of dates and the result is the same, after an edit the 'TO' date changes to 2008.