If a description has been added to a User Picker custom field, this description will not be displayed properly on pop up issue screens (eg. Create and Edit dialogs).

The plain text will always have <p> tags around it, and any Wiki markup will not be rendered.

Other custom fields such as a normal Text field do render correctly.

Comparison.png shows normal text without any formatting.
Comparison2.png shows text with the tags {color:blue} used.