When I edit the API Name for a custom field, it displays correctly, but when I refresh the page I see that the system actually appended __C to the name.

For Example:

In API names I edit the name of a field to be Plantango_Id 

When I click on Save the screen correctly displays the name

When I refresh this page, I see that the API Name is actually Plantango_Id__C

This is causing problems for me, since when you create a new field, the API Name does not have this trailing __C.  But if someone edits it, they can never get the name back to what it was originally.