my k4PC still malfunctions & amazon seem clueless - I actually called them while the faulut( see below) was repdoducible but thay had no idea how to trace it. saidd they';d escalate to developers but never heard back.
my fault is this - I buy a book, I see it download into K4PC then as soon as the blue progress bar is full, the book vanishes from my PC. I can force a resend from web page only to see the vanishing act repeat.
the fix is easy - I unregister from within K4PC, & select delete all local content, then reregister; book then arrives OK.
then the program will work ok for the next few free books before reverting to original fault. I think it happens only with azw3 books but that is unproven.
I cannot figure what in their screwed up code causes this. it is as if the program decides I am not entitled to the book after all & so deletes it