I'm check the residuals of a linear regression with Zivot & Andrews unit root test.

This is the plot: http://imageshack.us/f/840/zivot.png/

And the results are:


    > z <- ur.za(resid(mod), model='intercept')       
    > summary(z)
    
    ################################ 
    # Zivot-Andrews Unit Root Test # 
    ################################ 
    
    
    Call:
    lm(formula = testmat)
    
    Residuals:
        Min      1Q  Median      3Q     Max 
    -6.9484 -0.3336 -0.0052  0.3486  4.6749 
    
    Coefficients:
                  Estimate Std. Error t value Pr(>|t|)    
    (Intercept)  0.8358245  0.2559622   3.265 0.001145 ** 
    y.l1         0.9056053  0.0136199  66.491  < 2e-16 ***
    trend        0.0002781  0.0001612   1.725 0.084992 .  
    du          -0.9509595  0.2686740  -3.539 0.000427 ***
    ---
    Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
    
    Residual standard error: 0.8534 on 715 degrees of freedom
      (1 observation deleted due to missingness)
    Multiple R-squared: 0.9221,	Adjusted R-squared: 0.9218 
    F-statistic:  2823 on 3 and 715 DF,  p-value: < 2.2e-16 
    
    
    Teststatistic: -6.9306 
    Critical values: 0.01= -5.34 0.05= -4.8 0.1= -4.58 
    
    Potential break point at position: 21 


A potential break at position 21 seems correct, but the test tells there is not a unit root...so, how is it possible that the test "pass" for unit root checks but it also gives a potential break?
How to interpret the chart?

Thank you!