It appears when you have a project that uses multiselect custom fields, when you update the status of an issue in that project, any values in the multiselect custom fields disappears.

Note: This appears to be only multiselect, I changed one of our multiselect custom fields to a list, and the problem disappeared. Problem is that we need the multiselect fucntionality

Steps:
1) Create an issue, and select a value in a multiselect custom field pick list
2) Submit the issue, and then re-open it
3) change the status of the issue, and press the change status button
4) check value in multiselect custom field