The case of resource group names in IDs of disks are case insensitive. Steps to reproduce this issue -
Create a standalone disk in Azure, check for ID. For eg - "/subscriptions/subscriptionID/resourceGroups/diskRG1/providers/Microsoft.Compute/disks/TestVM_disk2" . Notice the case of resource group name -> "diskRG1".
Create a VM.
Attach the disk created disk (in step 1) to VM.
Go to newly created VM->Disks-> Check for the attached Disk ID and it displays as -> "/subscriptions/subscriptionID/resourceGroups/DISKRG1/providers/Microsoft.Compute/disks/TestVM_disk2" . Now the resource group name has changed to DISKRG1.
IDs of disk should be same and case sensitive. Is this a known issue ?