After using my custom Issue Types for a while, I decided to change the icons from the generic icon to another gif file. After changing the icon, all custom fields bound by the context of the Issue Types, were no longer displayed on the different screens (create, view and so on) Other custom fields used in other projects that were not using the mentioned Issue Types were still displayed correctly. A restart of JIRA made all the custom fields appear again. Though I did perform other administrative tasks at the same point in time, it looks like the problem is directly linked to the editing of the Issue Type, since other projects not using the edited Issue Types still worked fine.