When you create a custom field and give it a description, that description correctly appears under the field on all applicable screens. Editing the custom field description will work in a simple JIRA configuration (i.e. one project with one field configuration) but at some point this behaviour changed on me (I think it may have been as soon as other projects/field configurations were added). An update to the custom field description through the View Custom Field page no longer had any effect outside this page. At this point you must edit the custom field description in all appropriate Field Configurations (System > Issue Fields > Field Configurations and open the proper field configuration)
What I find frustrating is that there is no indication of this change and I spent a lot of time trying to understand why what worked before was no longer working.

I have no issue with updating the custom field description in the appropriate Field Configurations because this provides great flexibility (although could mean a lot of work if you have a complex environment). What I am hoping you can do is something to reduce the confusion when it stops working the way it initially did.

I would suggest:

• Providing an option to propagate the description - allowing you to select which field configurations would be overwritten
• A warning that the change will have no effect on existing field configurations (and therefore screens).

My preference would be the first suggestion as I believe it would greatly improve the user experience.

I hope I have explained this clearly.
Regards,
Jon