Router – Rip V2 not working as expected in simple network configuration

I am running into some problems, but I am not sure what is configured wrong. I have a simple network design as follows:

4 routers (connected via serial links) in a square'ish configuration with each router connected to a single switch (via FastEthernet). Here's an ASCII map

s---R1-----------------------------R2---s
     |                             |
     |                             |
     |                             |
     |                             |
     |                             |
     |                             |
s---R4-----------------------------R3---s

The subnets for the serial links are as follows:

192.168.1.0/30
192.168.1.4/30
192.168.1.8/30
192.168.1.12/30

The subnets for the Ethernet between the Router and the Switch are as follows:

10.0.0.0/20
10.0.16.0/20
10.0.32.0/22
10.0.36.0/22

I'm using Rip v2 for the routing protocol and I have configured each router as follows (in Cisco IOS)

router rip
  version 2
  network 192.168.1.0
  network 10.0.0.0

From what I've read, this should result in RIP sending out updates containing multiple (VLSM) routes for the 10.0.0.0 network. However, this is not the case. When inspecting the routes from the bottom left router, I see this:

R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.0.0.0/20 is directly connected, FastEthernet0/0
R       10.0.0.0/8 [120/1] via 192.168.1.6, 00:00:23, Serial0/1
                   [120/1] via 192.168.1.14, 00:00:12, Serial0/0
     192.168.1.0/30 is subnetted, 4 subnets
R       192.168.1.8 [120/1] via 192.168.1.14, 00:00:12, Serial0/0
C       192.168.1.12 is directly connected, Serial0/0
R       192.168.1.0 [120/1] via 192.168.1.6, 00:00:23, Serial0/1
C       192.168.1.4 is directly connected, Serial0/1

It shows the directly connected subnet as correct, by why is it displaying the rest of the 10.0.0.0 networks as NOT being variable subnetted. This same problem exists on all the routers. Each router is sending an update saying that it has a path to 10.0.0.0/8. Why are the routers not advertising the correct subnet. Shouldn't RIP v2 support VLSM?

Any help is greatly appreciated. If I am missing something simple, please let me know!