The only M codes that don't break the CV chain are M62 and M63.  M03 and M05 will.  If you think about it, you would never want the look ahead to turn your spindle off (M05) when the machine is actually still 100 lines back in the G code (assuming you have a 100 line look ahead set).  So when the interpreter look ahead runs up to a M05, it simply waits until all of the prior motion is complete (and it will be an exact stop) before turning the spindle off. 

The reason Pedio's code works is because the S word is given just once before a large set of G01 blocks.  CV is in effect for all of those G01 blocks. 

Steve