If the SPRINT field contains value and is correctly displayed on the issue screen, click Views->XML. The xml contains information about the SPRINT customfield but its value is empty.

This bug causes following issue with IDE Connectors:

• user opens issue in the IDE Connector (it is based on the issue XML view and contains information that Sprint value is empty)
• user makes changes and submit issue with the Sprint value empty
• the Sprint value is erased on the JIRA side (ups!)