This has been explained.
These devices have no state. There's nothing to poll. They just need to do their job. If you don't see them in the table, check again later. Zigbee is going to constantly adjust routes. If there's no path through the device at the current time, there might be later when the routes are adjusted again. If every time you check, it's not there, then you probably either need to join it again, or you need a stronger repeater.
Check out the Xbee for a strong repeater. They're a little pricey, but they work really well.
The IKEA repeaters are weak. They do work, but they're not strong, so I wouldn't be surprised to see devices not route through them if there's strong signal attenuation.
