LicenseRef-proprietary only recognised case-sensitively

https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-project_license says:

Custom licenses which are not in the SPDX registry, like proprietary licenses, can be denoted using the LicenseRef notation. LicenseRef-Proprietary can be used to denote a proprietary license, with an optional URL to the license text following after a = sign.

... but I published https://github.com/flathub/com.valvesoftware.SteamLink with LicenseRef-Proprietary, and it shows up in GNOME Software as "Free" (in the FOSS sense), which is misleading.

From a code search, it looks as though gnome-software wants to see LicenseRef-proprietary, with that exact case combination. I think it would be a better least-astonishment behaviour if it looked for that string case-insensitively.