If you are adding text to a map in the data view it will be added as annotation. There's is a difference between text (on a layout, like a title) and text in the data view (actually an annotation). The data frame has a default annotation group. The only way I can recreate the described problem is by adding text from the drawing toolbar when the default annotation group is turned off.
As a possible fix, go to your dataframe in the table of contents, right click and select properties:
Then in the properties dialog box choose the annotation groups tab and make sure the default annotation group is checked and click okay. Your text should appear:
