Note that this problem is not seen if all fields are taken from the table shown in the "Show Records from" entry in the previous screen. However, many people plan far enough ahead that they add fields from related tables at this point.
Thank you for your post.
The "Fields shown" pane in the New layout / Report dialog is too narrow to display field names as you describe.
I have forwarded your post to our Development and Product Management departments so they can consider making this dialog box resizable or adding tooltips in "Fields shown on layout/report pane" in a future release.
I encourage you to enter this information into our Feature Requests web form at:
The entries into this web form are monitored and read by Development and Product Management where they are then discussed and considered for future revisions. I could copy your post and paste it into the form, but there are additional questions asked that only you can answer.