Simple Time Formatted Plot Problem

[Fritz Sonnichsen]

I have played with this for a while. I have been able to plot time 
series data in the past but now something has gone wrong. I have 
distilled the problem into the short stretch of code below. The data 
plots without specifying the time axis, but when I add the time 
formatted axis it look find but the data does not appear.
  Any ideas?
Thanks
Fritz
======================= CODE ===========================
1;
clear all
fflush(stdin);

xtme=["12:20:39";"12:20:41";"12:20:42";"12:20:43";"12:20:44"];
xT=[    1      ;2       ;3       ;4       ;5];


plot(xT)
figure
timeFormat='HH:MM:SS';
xdatenum=datenum(xtme,timeFormat); %days from January 0, 0000
xlen = length(xtme);
plot(xdatenum,xT,'color','r');
datetick('x',timeFormat,'keepticks')
axis([0 xlen 0  10])
    return