emonBase sending no data with multiple emonTx

I have emoncms available on both .org and a Raspberry Pi and the same things occurs on both, so it isn't emoncms.

I have the OKG emonBase and two emonTx , when only one Tx is powered up, emonBase happily transmits the data every 6 seconds to emoncms. (either one, both work fine)

When both Tx are powered up, after a few minutes, emonBase stops sending data, turn either one of the Tx off again and the emonBase resumes sending.

The Tx's are configured as node10 and node11, I have made no modifications to the NanodeRF_multinode sketch (save setting it to 868mHz). Interesting that the sketch says:

#define MYNODE 15    

and yet emoncms reports the temperature sensor on the base as node20_1

To try to resolve the data transmission problem, I configured the sleep interval on node11, it's better, however it sitll sometimes stops sending the emonTx data for up to 10 minutes.

emonGLCD is working just fine, and is regularly updated from the emonTx.