Using version 2.1.35 on Mac. To reproduce:
Go to Manage Note Types, select a note type and click “Cards” to open the cards window
From the pulldown, select “Rename Card Type”
Enter a new name and click OK
You get the warning dialog, “The requested change will require a full upload…”
However, when you sync it doesn’t bring up the conflict dialog, it just syncs normally, and all other devices also sync normally without the usual “download from/upload to” dialog. The new name is reflected normally on other devices. It appears that the warning dialog is presented in error in the desktop app.