Listen!  My pronounciation “EeshaavaaSHyam” (ईशावाश्यम्) is also “paata bhedha”.  How I heard from my masters, I am repeating.  But, actually, it is “EeshaavaaSyam” (ईशावास्यम्) – “S” (स), not  “vaaSHya” (वाश्य).  My masters, they used the same “SH” (श) for “vaaSya” (वास्य) also.  I am retaining the “paata bhedha” as it is, as a respect and reverence to my masters’ way of pronouncing it.  In Vedic Tradition it is allowed; the “paata bhedha” which you heard exactly from your master is supposed to be retained as it is.  So, even though the letter here “EeSHa” (ईशा), the “SH” (श) is different, “vaaSyam” (वास्यम्), the “S” (स) is not the “SH” (श), but because I heard from my masters – “EeshaavaaSHyamidham Sarvam”  (ईशावाश्यमिदं सर्वं), I am retaining it.  So, all my disciples are requested to retain the same “paatta bhedha” of my masters.  It is a way of giving respect to the teacher.  The highest place given for the masters and teachers in our Vedic Tradition: even if there is pronounciation difference, it is accepted and revered as “paata bhedha” of that Master.  And I do want to keep that tradition!