The "Fields" in the context browser you are referring to relate to the Environment Library.  The Environment Library relates to the String Table, but they are not the same thing.

The below is an excerpt from a blog entry here on the UG (http://k2underground.com/blogs/fromthebench/archive/2008/04/01/how-to-programmatically-access-environment-settings-within-blackpearl-process-code.aspx):

"There is an environment library server containing the fields, values and Environments that you see exposed via the K2 object browser. Then there is the String Table which resides in the K2 workflow server and can by managed by the workflow management tools found in K2 Workspace.  When you export a process, String Table variables will be created from the Environment variables that you have used in your process. After the export, there is no further "link" between the Environment variables and the String Table fields.  Exporting the process again with different Environment library values will override the values in the String Table for the selected environment. Changing the values in the Environment library without exporting will NOT automatically update the String Table values."

HTH.