There are projects and workspaces. Projects have files and/or folders added in the Project Settings dialog window which are listed in several windows like on tab Project in File View. Workspaces are projects without having project files added in Project Settings dialog window.
The project files/folders and everything else customizable in Project Settings dialog window are stored in the file ProjectName.prj. This file can be even manually edited by clicking with secondary (right) pointing device (mouse) button on the project name at top of the tab Project in File View to open the project context menu and click with primary (left) pointing device button on context menu item Edit project file. However, a manual edit of the project file should not be done except the user really knows what to edit. It is better to use the Project Settings dialog window to make changes on project file.
The workspace settings are stored in the file ProjectName.pui. The file extension pui is an abbreviation for project user interface. The storage location of this file and its exact file name depends on the last two settings at Advanced - Settings or Configuration - File handling - Advanced. It is stored in the same directory as the file ProjectName.prj and has the same file name with just different file extension ProjectName.pui on only last but one configuration option Save project information for use on multiple systems is checked.
The project user interface file stores on closing of the project/workspace all information required to restore the workspace on next opening of project/workspace. The stored data are the full names of all files currently opened in the order as currently opened, which file is the active file, where is the caret positioned in each file, the window position, width, height and mode (normal, maximized, minimized) of each opened file, folds, bookmarks, etc. There is always first closed a currently opened project/workspace with storing the workspace that into the .pui file before exiting UltraEdit.
There is only the configuration setting Close all files when opening or switching projects at Advanced - Settings or Configuration - File handling - Miscellaneous This setting checked results in first closing the currently opened project/workspace on one being opened at all and next also in closing all currently opened files before opening (another) project.
Peter, what you would like to have would require an option called, for example, Close all non project files before closing project. All currently opened files which are not project files according to files/folders added to .prj file would be closed by UltraEdit before closing the project with updating the data in the .pui file on having this option checked. But such an option does not exist in UltraEdit v26.20 and also not in UE v28.00. I think, best would be if that option is a project option in Project Settings window and not a configuration setting for a maximum flexibility as this option would make never sense for a pure workspace. Please request such a project option feature by email to IDM support if you would like that in a future version of UltraEdit.
There is currently only the possibility to open all the project files to work with, order them as wanted, put the caret in each file to line/column as wanted, close the project and next set the read-only attribute on the .pui of this project. In this case UltraEdit does not write silently any workspace data into the project user interface on closing the project (and exiting UltraEdit). In other words the workspace is frozen (write-protected/read-only) and therefore the project is opened always with exactly the same workspace.
Best regards from an UC/UE/UES for Windows user from Austria