Hi John,
Crystal Reports will display the Group Header without a Details Section being printed.
Here's a workaround:
1) Create a formula called 'FakeGroup':
whilereadingrecords;
"";
2) Create a group on this formula and make sure this group sits above the existing Invoice Group
3) Suppress Group Footer 1
4) Go to Group Expert > Select the Fake Group > Options > options tab > check 'Repeat Group Header on Each Page'
5) Move all fields from Group Header 2 to Group Header 1
6) Suppress Group Header 2
Let me know how this goes!
-Abhilash