V26.5.1 Path re-open after using pathfinder tool
V26.5.1
The steps you were taking when you experienced the issues:
1. pen tool to do a open path
2. close the path using "add to shapes" in pathfinder 
3 use pen tool to start a new point,  the previous closed shape will reopen and join the new point
Your expected result :
using pen tool to start a new point should give a single point, not joining the previous closed shape
the closed shape should remain closed
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       Ten_A
    
 commented Ten_A
    
 commentedI often interrupt path editing by pressing the "esc" key. 
 In this case, We can press esc key before apply pathfinder.
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      Thanks for raising this up! I confirm this. 
 Disabling Rubber Band for Pen in Preferences > Selection & Anchor Display does not help.The bug is pretty old and is reproducible since at least CS4 (but is absent in CS2), right after Pathfinder Unite/Add learnt to close opened paths. A known workaround is to deselect the closed object before you start to draw a new path. 
 
           
              