This problem was identified by Andy Carter and explained at
https://list.scms.waikato.ac.nz/mailman/private/greenstone-users/2008-March/006536.html
The explanation below is excerpted and slightly paraphrased from his message in the mailing list:
The matter concerns Greenstone 3. When using GLI:
"The issue is the "display text" fields in the Search area under the Format tab.
It is not possible to save the text in the "display text" fields. Each time GLI
is opened, the "display text" fields are blank. And even if text is entered in the
fields and we do a rebuild, nothing appears."
The search forms in the Greenstone 3 browser interface do not change the display text fields to take into account the changes made through GLI. This is only in Greenstone 3, whereas it works fine in Greenstone 2.