Folder redirection destroys icons

Greetings,

I have a Synology DiskStation NAS device on my home network used to store
data shared across the network.

On the machine I'm using to manage music and picture libraries, I've
redirected the Music and Pictures folders to the NAS volume (mapped as
Z:\Pictures, Z:\Music respectively).

The shared volume on the device has full RW privileges for all users.

After using the "Location" property of the Pictures and Music folders to
change their location, and copying all contents to the new location, I find
that the Music and Picture folder icons have been changed to the default
yellow folder representation.

Why is this happening and is there a way to fix it while still keeping the
folder redirection?

Are there any specific caveats I should have taken into account when
redirecting user folders to a NAS device?

thanks