Clustering - neighbours bleed across non-overlapping boundaries when more than one spatial condition is used

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What steps will reproduce the problem?
1.  Run a cluster analysis using a non-overlapping spatial condition as the 
first condition, then sp_select_all() as the second (or some other condition).  

What is the expected output? What do you see instead?
The cluster analysis should contain a sub-tree constrained within the full 
tree.  The issue is that the sub-tree is not so contained, and instead has 
values from all across the data set.  

This appears to be something to do with how the linkages are being run.  
Matrices are being built correctly.  

Original issue reported on code.google.com by shawnlaffan on 19 Aug 2013 at 5:41