I've heard of it when:
– The editor is working on an Assignment file (ICMA) and the designer did not update the assignment file in InDesign. (In InDesign, saving changes to the INDD file via File > Save does not save changes to the Assignment file. Look for little yellow Out of Date triangles next to assignment names in your Assignments panel to see if this is the case.)
and when:
– The editor is working on the Layout file (INDD) in InCopy and the designer did not save changes to the INDD file in InDesign … editors can't see any changes the designer hasn't saved to disk yet.
and when:
– The editor is working on the Layout or an Assignment file, designer has saved all changes properly, but the editor forgets to choose File > Update Design in in InCopy. This would only happen if the editor has the file open concurrent with the designer saving changes. They should see an “Out of Date” message appear in their title bar. Choosing Update Design will fix it, also, closing and opening the file will fix it.
hope that helps!
AM