Example scenario: I have "Tower 1" and "Tower 2" models open in the same session of Revit. They both have the "Pedestal" model linked in. In another session of Revit, I (or another user) make changes to the "Pedestal" model. I want to Reload it in BOTH "Tower 1" and "Tower 2", but CANNOT - get the WARNING: "The link cannot be reloaded because it is loaded into another open document." The WORKAROUND: close all models except one, Reload the link, then re-open the other models.
Autodesk's stance: "This is expected behaviour with Revit and linked models. ...use multiple sessions of Revit."
NOTE: You also get the same error message if you try to insert a link that's loaded into another model (for example, when setting up the "Tower 2" model in the example above, if the "Tower 1" model is setup and still open), but it loads it anyway! Maybe the "The link cannot be reloaded because it is loaded into another open document" message is for the future?
And you get NO error when opening the models in the first place (although it doesn't open the "new" version, if the file's been changed since it was last loaded into the already-open model - i.e. it uses the same/old version of the link for all).
As annoying as it is to not be able to work on the link in the same session (and therefore not be able to copy things between the models), it's frustrating that Revit can figure out how to load the link the first time, but not the second! WHY?
If it's using the same version of the link for all open models, why not just allow reloading w/ a warning dialog that says "Reloading this link will reload it for ALL open models" (and maybe list which ones it will affect?).
While you're at it, if you could check/notify when opening the second model, too, that would be great! "The model being opened contains a link that has changed since being loaded into an already-open model. Would you like to reload the link for all open documents or use the old version for the model being opened?"
BTW, if there's a circular link when opening the 2nd model, it displays an "Unresolved References" dialog instead of the "Circular Link Conflict" dialog.
And I'm sure the response will be that making this change is "not trivial" because they'd have to figure out what to do about any warnings generated in ALL of the host models when reloading a link - and what would happen if you process them in one model, but then cancel in another... of course, keeping links in separate spaces would fix the problem (though increasing the memory footprint) and allow the link to be open directly, too!
