This is actually happening in libc/net.
inet_pton4() uses the .'s as a way to figure
out how to assign dotted-decimal. 

The "work around" is to assign this way:

deimos# route add -net 224.0 127.0.0.1
...
deimos# route show
Routing tables

Internet:
Destination       Gateway            Flags 
default           10.129.1.4         UG     
10.0.0.0          link#1             U      
10.129.1.4        00:b0:c2:89:af:1b  UH     
10.129.1.7        00:b0:d0:e1:5f:44  UH     
10.129.10.5       00:b0:d0:de:49:df  UH     
loopback          127.0.0.1          UGR    
localhost         127.0.0.1          UH     
224.0.0.0         127.0.0.1          UG  

Otherwise, just using 224 causes inet_pton4
to translate it differently. I don't really
see a way to "fix" this.

I will close this in awhile if no one objects.