Well, at least it's doing so for errors from ActionTypeService implementations. Hopefully this one is not a dupe because I think I recall a discussion about something similar at one point but couldn't locate a similar jira.
At any rate, if I have a custom ActionTypeService with a validate method like this:
Then if the validation fails, instead of getting the expected error messages, I see something like the attached image.
RemotableAttributeErrors are intended to hold fully resolved messages as opposed to message keys that get looked up in a resource file. One of the main reasons being that they are intended to be "remoted" so whereever those errors end up, the consumer probably won't have whatever message key was being passed in order to resolve it (hopefully that makes sense).