I have got it -- the index less Section is too far down!!
Yes! Decalring the shared variable as volatile is not enough to preserve the values. Processing of the shared variable in the main code should be done after disabling the interrupt logic momentarilly to understand which a reader needs to have kowledge on AVR ASM Programming. Probably, we could avoid it should the AVR support the incrementing/decrementing the variable keeping it in memory as is done in 8085 (INR/DCR M).
Thanks for the guidance.