All credit for this goes to MZ1987, who posted this procedure here. I am documenting it in my blog to make it easier for me to find in the future.
- Open the model with Specify.
- In the Opening Worksets dialog, select all user-created Worksets and choose the Open button. The values in the Opened column should all be Yes.
- After the model opens, open the Worksets dialog. Select all of the user-created worksets and select the Editable button. Set the Open/Close state of each Workset to the way you want it to default in the Opening Worksets dialog. [This is the key step.]
- Synchronize the model, using the Synchronize and Modify Settings option, NOT Synchronize Now. In the Synchronize with Central dialog, make certain that the User-created Worksets toggle is checked.