If you try typing Coffee Corner in any of the tag selectors (which have type-ahead active) - there will be no results, so it is not possible to select it as a tag. If you follow the tag or if you were active in Coffee Corner - like me, you will see it in the drop-down list after clicking on Choose from your followed and most used tags. The entry is selectable:

If you try saving the question with Coffee Corner as a primary tag, you will see the following error message:

Scroll down and you will see the actual error:

It is possible to bypass the problem and still post with Coffee Corner tag - just use it as a secondary tag and select something else - e.g. Using SAP.com as a primary tag.

The current question is an illustration on how to reproduce the problem - for @jerry.janda