Maybe all PC drives will work this way until the proper mod is done. The 357 is easy to work on but I can't find the RY/DC etc. marked. I don't know how to get the JU-257's apart without destroying very fine ribbon connectors.
Before you mod a PC drive disk change is on pin 34. You can use a cable/motherboard hack to connect it to pin 2 (the later is what amiga technologies did). However this won't work with alot of games due to the missing ready line. By jumpering the drive to put ready on pin 34 you just need to find the disk change and put it on pin 2, you can go from the jumper pad to do it. Everything you're experiencing is normal for how you've got the drive setup.
My Amiga Technlogies A1200 came with a JU257A605P, which I seem to remember was a bit of a pain to hack. Partly because I didn't want to break it and partly because there were no guides for that drive at the time. They look fragile but if you're careful then you should be fine.
http://www.softpres.org/article:hard:modifying_the_pansonic_ju-257a605p_fdd http://amiga.serveftp.net/FloppyConversion.html
