title: Error when plotting a segmented regression object
body: <p>I am running piecewise regression on some binary logistic regression in program R using the package 'segmented'. I have chosen a final model and now want to plot the predicted probabilities and confidence bands. My final model has one continuous variable that I am segmenting the regression line on as well as two dichotomous factor variables. Here is some output so you can visualize the structure of the model</p>
  
  <pre><code>Estimated Break-Point(s):
     Est. St.Err 
   3.799  1.117 
  
  t value for the gap-variable(s) V:  0 
  
  Meaningful coefficients of the linear terms:
                 Estimate Std. Error z value Pr(&gt;|z|)  
  Intercept)     -0.4056     0.4199  -0.966   0.3341  
  approach_km     -0.4970     0.1963  -2.532   0.0114 *
  sea2             0.8760     0.3989   2.196   0.0281 *
  grp.bin2         0.4534     0.3320   1.366   0.1720  
  U1.approach_km   0.4969     0.1967   2.526       NA  
  sea2:grp.bin2   -0.8481     0.4731  -1.793   0.0730 .
  </code></pre>
  
  <p>Here is a plot of the predicted probabilities and the 95% confidence bands</p>
  
  <p><img src="https://i.stack.imgur.com/GvvR6.jpg" alt="first estimated probability plot"></p>
  
  <p>Next I wanted to re-level the dichotomous variables and plot another line to show how the probabilities change based on what group you are in. I re-leveled the variable grp.bin and plotted the probabilities and confidence bands. This obviously changes the coefficients in the output of the model and changes the prediction line. It does not however change the plot of the confidence bands.</p>
  
  <p><img src="https://i.stack.imgur.com/6McIM.jpg" alt="second probability plot"></p>
  
  <p>So my question is...Does the plot.segmented function plot the widest confidence bands associated with all combinations of the predictors or is there something wrong with either my coding or the function. I can add my code if needed but the prediction lines and 95% confidence bands are just plotted using the plot(segmented.object, add = TRUE) function to add them on top of the observed data points.</p>
  
  <p>FYI, another combination of the variables yields a maximum probability of flight of 0.23 (if I plotted that it would hug the bottom confidence band).</p>
  
  <p>Thanks</p>