This still puzzles me that if my reset configuration is not proper, why should i get my normal code running while I should get in to the bootloader!!
resetting a mkicroprocessor is a complicated thing and just visualize the following 'stupid', nonverified and probably incorrect example.

Two thing in the uC has to reset within one microsecond for the ISP to catch. One require 2.2V to reset (which is within tolerance) the other require 2.4V to reset (which is within tolerance). Now with a RC reset it can take more than 1uS to go from 2.2 to 2.4V whereas the reset coming out of a supervisor has a risetime if a few nanoseconds.

Erik