Variables Multi-value not working with Graphite tags

Trying to create a variable based on Graphite tags.
data in Graphite is tagged i.e. I have data with tags such as
region=amrs;device=router-x
region=emea;device=router-y

First variable named = region
query = tag_values(region)
this returns a list with values “emea” “amrs”

I want to pass the $region variable to next variable query

Second variable named = device
tag_values(device, region=$region)

when I view the template the variables are set correctly
for example in the region variable I see “emea” “amrs”
when I select “emea” I see the device list populated with “router-y”
when I select "amrs I see the device list populated with “router-x”

however when I select region=ALL the device list shows “All” and not “router-x” and “router-y” as I expect.

when I use multi-select and select region=emea + amrs the device list does not update, I expect it to update to show device “router-x” and “router-y”

thanks