DNS (GTM) whith secondary IP address (network) in one ISP router

i have a gtm module deployed with two links and its working, one of those links have an ISP router with two segments (primary ip and secondary ip in the same layer 3 interface) and i have vservers in both segments, in order to automatically detect the link for each vserver i've added a self-ip with address in the secondary network and added the secondary ip in the router address box in the link configuration page. The vserver link auto detection works fine. Also I have an icmp transparent monitor defined for both link, the link with one ip address in the router address box works fine, but the other one with secondary ip address fails some times, with a message in the gslb log saying that monitor fails UP->DOWN reason (no route) and after that other log entry that say the monitor succeeds DOWN->UP. what i'm doing wrong?