Xbee strange behavior

Hi all,

I am doing a home automation system with Xbees series 1. I have an arduino base the has the xbee coordinator and in my system has 2 standalone xbees that aswer only to the coordinator.

The standalone xbees only toggle the relays on/off, both are configured to detect pin change on D1, where there is a push button, and I am using a android app that I made with only 2 buttons to send commands to arduino via ethernet shield, when the arduino receives these comands it sends a command to the xbee.

It works really great when I send commands to only one xbee or using the push button to toggle the lamps, even if I push one button from xbee at a time, but very fast. The problem is when I try to send commands to the xbees from the app. When I send a command to only one, it works as expected, but if I send a command to each one with a short delay (the time that I spend to click on one button on the smartphone's screen and then on the other) the xbees blinks the rssi led for a while and do nothing, but if I wait more or less 2/3 seconds they works again, but only with a little delay between I send a comman to one and then to the other.

If any smart guy that have experience with xbees could help I would appreciate it.