I have the same issue. I get this when I attempt to bulk delete the demo Contacts, Accounts, or Cases loaded when I first installed. I will check off one contact, account or case, choose bulk action - delete, and it works fine. When I check off two or more, it redirects to index.php and only deletes the first contact, account or case, not all of the ones I checked.
Bulk delete of Opportunities, Leads, Calls, Meetings, Tasks, Notes, works fine, no redirect and they all delete.
When I create a Lead then save, it will redirect to a blank index.php page. I also noticed that it did not save the email address. I tried to edit the lead and save, and it redirected to the blank index.php page and did not save the email address again. All other info for the lead was saved.
I have a feeling that there are more sections related to the contact, account, case, or lead sections that run into this issue, of which I have not tested every part just yet.
Other issues (not sure if related): log shows that the versions table is not found;
I did repairs and rebuilds, as well as upgrade to 7.9.9 from 7.9.7 successfully. Still the same issue.
Did you, or anyone, find a solution?
PS - Irony - I tried replying to this thread twice now, and my reply didn’t save, and it redirected to the main page… Crazy.