[Bug] Existing query params lost when entering loading route

[jrjohnson]

🐞 Describe the Bug

When an index-loading route is entered during a query param only transition the existing QPs are lost and only the newly set param is retained.

🔬 Minimal Reproduction

I've created a reproduction at https://github.com/jrjohnson/qp-replacement-loading-route-reproduction running the tests will show the failures. You can also navigate to the broken route and click the query param setting buttons.

😕 Actual Behavior

Setting a QP re-sets the existing params to their default value.

🤔 Expected Behavior

Setting a new param should not change existing params.

🌍 Environment

• Ember: - 3.19.0
• Node.js/npm: - v12.18.2 / 6.14.5
• OS: - OSX
• Browser: - Chrome / Firefox

➕ Additional Context

This was originally reported as a new issue with 3.13 by @jakebixbyavalara in #18683 but I wasn't able to find a linked issue.

Tagging @pzuraq as he was involved in the original issue (and this is probably a result of tracked properties for QPs being introduced in 3.13).

[jrjohnson]

I'm no longer sure this is a 3.13 issue, I went all the way back to 2.18 and it still happens there. I've never had a loading route on both an index and main route before with query params so I'm not sure this has ever worked. It still reads as a bug to me, but maybe not a new one.

[rreckonerr]

Ran your reproduction on 3.27.0 and seems like it's already fixed

[jrjohnson]

Agreed! Working with 3.25.1 for sure. Thanks for updating!