pt-sift disables echo on OS X if there is a single timestamp

On a system with this info:

telecaster:pt-stalk-samples fernandoipar$ uname -a
Darwin telecaster.local 11.4.0 Darwin Kernel Version 11.4.0: Mon Apr 9 19:32:15 PDT 2012; root:xnu-1699.26.8~1/RELEASE_X86_64 x86_64
telecaster:pt-stalk-samples fernandoipar$ bash --version
GNU bash, version 3.2.48(1)-release (x86_64-apple-darwin11)
Copyright (C) 2007 Free Software Foundation, Inc.

If I run pt-sift (as obtained just now from percona.com/get/pt-sift) with only one timestamp in the captures directory, echo is disabled on the session. Executing the 'reset' command on the shell solves the problem.

If I run the script with two or more captures, I don't have this problem. I have been able to reproduce this with multiple captures but just in case (as I couldn't find one in the tests directory) I will be attaching a sample capture that can be used to reproduce this problem on a similar system.

I haven't tested this on other platforms yet.