Text-in-a-shape can be put on Path, but loses the textPath when saving

Steps to reproduce:

• open Inkscape
• switch to text tool
• click, drag a text box, then type (multiline is more interesting)
• switch to Bézier tool, draw a curved path
• select both objects, Text > Put on Path - now even multiline text can be put on a path. Is this correct according to the specification?
• save, close, reopen

What happened?

Text has lost the connection to the path.

What should have happened?

Text-in-a-shape should either:

• refuse to be put on a path
• be converted to normal text, with loss of line breaks
• if the specification allows it, keep its textPath tags on save (not allowed, see Tav's comment below)

Inkscape Version and Operating System:

• Inkscape Version: 1.0beta1 (41b54024, 2019-11-21)
• Operating System: Linux Mint 19.2

Reported by Thomas1966 in the forum: https://inkscape.org/forums/Deutsch/gruppieren-text-am-pfad