Updating Ticket Custom Field

Hi all,

I have a strange problem when I am updating a Ticket Custom Field. The
field is a ‘Select one value’ type.

Whenever I change it from one value to another(say, value1 to value2 but
not ‘no value’ to value1 nor value1 to ‘no value’), the following
message will be displayed at the top of the Ticket display frame:

 * Custom field value value1 could not be found for custom field Myfield

The custome field value is updated. But such a message is quite annoying
and misleading.

Is this a bug? How can I get rid of it?