XBEE ATEA incrementing without sending

XBee & XBee Gateway XBee - 802.15.4
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1

I have an XBee Pro (XBP24-AWI-001) that just sits listening to data packets being sent to it by other XBee Pros(XBP24-AWI-001)
I keep checking the EA parameter and find it is constantly growing, even though the XBee is not being told to transmit anything.
Is there a reason for this?

Firmware is 10EC

2

This problem is the same issue as my other question (solved)
http://www.digi.com/support/forum/35296/xbee-sending-ack-failures-without-ever-being-told-transmit