Hi All,
I have noticed that when you set default values for some items in blueprints, if they are contained within folders that have brackets (or any other non-alphanumeric character despite some being permitted for naming purposes), then this will cause an issue.
Best thing to do in that case is ensure any containing folder above the blueprint does not have any non-alphanumeric characters. If so, simply rename the folder, restart the editor and try again. I had an issue just like this, but I had a bracket in my folder name two levels above the blueprint. Renaming did the trick for me. Perhaps this may be of use to someone. This comment does not directly answer the exact question, but is very close in nature - so others might find this useful.