We can have an uppercase member interface in the bridge config
bridge br1 { enable-vlan member { interface Vxlan1 { } } }
But an upper case VXLAN interface can not be created.
During debugging of this I also noticed that there are multiple different calls to confi.exists() in vyos.configdict - some use string, some use list as argument.
This has been streamlined to only make use of lists.