I'm going to guess this is a result of the Highlight feature which allows issues to be greyed out based on criteria in a context.
The feature is documented at http://confluence.atlassian.com/display/GH/Using+Contexts+to+Filter+and+Highlight+Issues
I hope this helps,
@webwesen Your update points to the source of the issue, though it could be caused by any plugin introducing a certain library. We have a fix for the issue and it will be available as soon as possible. Please follow the following issue: https://jira.atlassian.com/browse/GHS-9730
...It's true that there are projects in Jira; but they are merely a way to cut off issues, to tell them apart from other sections of work and to apply rules that are specific to that team (the schemes)....
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