Using CC2019 on a Mac running High Sierra

Steps to reproduce:
1) Create a document with a few hyperlinks in it.
2) Whilst this document is open, open a 2nd document, and copy/paste the links from one document to the other.
3) Save both and close.
4) Trash source document

Expected result: hyper links should work in Target document as expected.

Actual result: hyperlinks all appear broken in document. Whilst an exported PDF appears to still work, ID reports all those links as broken.

Other details:
If you retrieve the source document from the trash, it the links in the target document suddenly start working again, meaning your not actually pasting the hyperlink, but theres some sort of link that exists between the source and target document.

Saving target file as a new file, saving as idml, has no effect – those links are still tied to the source document.

This in an absolute tragedy if you are working on large documents with lots of links, and needs fixing ASAP