I select the content type, filter, select and delete the page using the dropdown menu, then the filter resets and I again have to select the content type in the filter because I am not finished. 

The filter should remember the settings until it is reset.

Comments

Yes, that seems like an oversight in the core's Bulk Operations views fields. 

A workaround is to use the contrib Views Bulk Operations instead. You'll need to:

  1. Edit the View that shows the content (admin/structure/views/view/node_admin_content/configure/page)
  2. Remove the field called "Content: Bulk operations"
  3. Add the field called "Views bulk operations: Content"  (notice that, even though the fields are name similarly, they ARE different). Choose the operations you want to expose

That will respect the original terms of the search when you go back after deleting an item.

I would also suggest opening an issue in the core issue queue. You'll need a github account.

By the way, be aware that Backdrop version 1.28.1 has a bug that prevents the opening of the Views fields UI sometimes. You can try and patch your version manually as shown here, or revert to version 1.28.0. There will be a release soon.