Mismatch ClientTransactions from multiple INVITEs

I am experiencing the following conditions:

(1) Occasionally, repeated invocations to
SipProvider.getNewClientTransaction() (using different INVITE Request
instances) return the same ClientTransaction instance.  (BTW, the
invocations originated from different threads but against the same
SipProvider instance.)  I was expecting different client transactions.

(2) SipListener.processResponse() is invoked with a ResponseEvent e, such that:

e.getResponse()'s "Call-ID" header field does NOT always match
e.getClientTransaction().getDialog().getCallId().

(Needless to say, the Dialog's application data can not be relied upon
in these cases.)

Has anyone seen this?  I used
[http://is2.antd.nist.gov/pub/nist-sip/proxy-libs.zip].

Kalman