Unrelated call to readBytesUntil breaks xbee

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What steps will reproduce the problem?
1. Connect xbee via hardware serial
2. Connect something else via SoftwareSerial and call readBytesUntil
3. Call xbee.send

What is the expected output? What do you see instead?
If readBytesUntil has not been called, the packet is successfully sent.  If 
this has been called before, the call never returns.

What version of the product are you using? On what operating system?
It is unclear how to determine version of the Xbee library, as there is no 
versioning header in xbee.c or xbee.h

Please provide any additional information below.
I've narrowed it down to the readBytesUntil call.  Having the SoftwareSerial 
port change its listening status does not create the behavior - only the call 
to the Stream derived function.

Original issue reported on code.google.com by [email protected] on 1 Oct 2013 at 9:33