Cisco Firewall :: ASA5510 Static Routes For Management Interface Not Working

We have several pairs of ASA5510s in failover A/P mode, some running 8.3(2) and others running 8.4(1).
 
e0/0 = outside
e0/1 = inside
m0/0 = management
 
The problem we're having is we can't get anything to route out of the management interface unless we put in a static route at least to the subnet level. For example, we want syslog traffic to exit out m0/0 to our syslog server 10.71.211.79. Our 'gateway of last resort' points to the next hop out e0/0, and a second static route with a higher metric and a more distinct network space is for m0/0 as in:
 
route outside 0.0.0.0 0.0.0.0 192.168.49.129 1route management 10.72.0.0 255.255.0.0 10.72.232.94 10
 
This doesn't work, and ASDM loggin gives this error: ".....Routing failed to locate next hop for udp from NP Identity Ifc:10.72.232.89/514 to management:10.72.211.79/514"
 
If I put in a more granular subnet route, or a host route of the syslog server it works, such as:
 
route management 10.72.211.0 255.255.255.0 10.72.232.94 10   <------------- this works
 
route management 10.72.211.79 255.255.255.255 10.72.232.94 10   <------------- this works too
 
Why won't a static route for 10.71.0.0 255.255.0.0 work in this case?
 
We are going to have numerous hosts access and be sent messages though the management interface of these ASAs, and it would be very burdonsome to have to add a host, or even a subnet, route for every one. I've removed all static routes and tried to rely on EIGRP, but that doesn't work. I also had to put 'passive-interface management' under the EIGRP for this to work.
 
Here is the pertinant ASA config concerning syslog, routing, and interfaces:
 
interface Ethernet0/0 nameif outside security-level 0 ip address 192.168.49.140 255.255.255.128 standby 192.168.49.141 !interface Ethernet0/1 nameif inside security-level 100 ip address xxx.xxx.xxx.xxx 255.255.255.128 standby

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