I have seen reports that the boot vector does not always get properly written with ISP and that it is advisable to write it several times and verify it before exiting ISP mode.
I have seen no reports to that effect; however RC reset and abort of ISP has done it. If you can write it once it IS written, the write many times is an urban legend resulting from someone being lucky after doing so.

If you use NoTouch and/or "the backdoor" you can forget about all that business it just works every time

Erik