Following the repro, a temporary copy of a BP Macro library is loaded into memory. When you right click to place a node, it incorrectly lists macros defined in this temporary library. They are fully placeable and it will save. However if you transfer this to another machine or delete your temp folder, that macro will break as it is pointing to an invalid library.
In my testing diffing BP Function libraries and individual BPs did not expose the temp functions, so it might be a macro-specific issue.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-107568 in the post.