Meaning of pterms in survreg object?

I am trying to model survival data with a Weibull distribution                                                                         
using survreg. Units are clustered two apiece, sometimes receiving                                                                     
the same treatment and sometimes opposing treatment.                                                                                   
                                                                                                                                       
Residual and predict methods are not carried out on the survreg                                                                        
object, although the component linear.predictors exists for the                                                                        
survreg object. Looking at the code I see that the residual method                                                                     
refuses to run if any of the components of the pterms vector is                                                                        
equal to 2.                                                                                                                            
                                                                                                                                       
When taking the logarithm of the data and trying a linear mixed                                                                        
model, residuals and predicted values are produced just fine.                                                                          
                                                                                                                                       
So what is pterms and why is it that, when any component of it                                                                         
is 2, residuals are not allowed to be displayed?

Johannes H?sing               There is something fascinating about science. 
                              One gets such wholesale returns of conjecture 
mailto:johannes at huesing.name  from such a trifling investment of fact.                
http://derwisch.wikidot.com         (Mark Twain, "Life on the Mississippi")