Instant On - Wired

Hello community, 

i was wondering about an issue i stumpled over with my switch setup. Its like so:

I have a main Instant On 1830 8G POE switch where my router, access point and nas is connected to. 

Also connected are two Aruba 2530-8G switches fo other rooms. 
I use 3 VLANS. Main default VLAN 1, Management VLAN 10 and Guest VLAN 20.

The 1830 should be Spanning Tree Root Bridge for all VLANS at all times, because this switch is on USV and always on. 

So i set bridge priority 4096 on the 1830 switch and higher values (priority 3 = 12288) on the 2530 switch.

Unfortunately as i can see in the CLI over SSH on the 2530 switch the 1830 switch only becomes root bridge for the default VLAN 1. 

For the VLANs 10 and 20 the 2530 switch becomes root bridge, even if i set the maximum value which is priority 15 = 61440.

I see no way to set the bridge priority for VLANs on the 1830 switch. 

So how does the Instant On 1830 switch handles Spanning Tree for VLANS?