Go CCIE Go!! - A Cisco Certified Internetwork Expert

Hi All,
I am guessing this must have been asked before … but I cannot locate it … apologies in advance for asking again.
I have been struggling to get inverse arp on a specific DLCI to come up unless I specify it using “frame-relay interface-dlci [dlci] in the config .. eg:
R1 (connected to Frame switch with DLCI 102 103 104 105)
interface Serial0/0 encapsulation frame-relay ip add 12.12.12.1 255.255.255.0 no frame-relay inverse-arp ip 103 no frame-relay inverse-arp ip 104 no frame-relay inverse-arp ip 105
R2 (connected to Frame switch with DLCI 201 203 204 205) interface Serial0/0 encapsulation frame-relay ip addresss 12.12.12.2 255.255.255.0 no frame-relay inverse-arp ip 203 no frame-relay inverse-arp ip 204 no frame-relay inverse-arp ip 205
This senario produces no maps no matter how long I wait …
However adding :
R1 Serial0/0 frame-relay interface-dlci 102 R2 Serial0/0 frame-relay interface-dlci 201
and it springs into life.
I believe the additional config is unnecessary but for the life of me I am baffled as to why.I need it.
Routers/IOS are 3640/12.4.8d and 2811/12.4.10c
Thanks in advance
Mick