IIGS says it's HFS but Mac says ProDos!!!

[fermilevel@aol.com (FermiLevel)]

I am having a strange problem with one particular 135 Mb cartridge for my
new EZ135.  This cartridge came formated HFS by SyQuest that was perfectly
readable by my Mac Duo 280c.  I then formatted the cartridge from my
IIGS/RamFast as a 135 Mb HFS volume with no problems.  BUT, now I can't
get my SYSTEM 7.5.1 Duo 280c to see the volume!  When I use some shareware
utilities such as Mount Everything, it shows the cartrige to be an Apple
Prodos volume!  When I try to format from the Mac from the Mount
Everything utility it tries to make me enter a password, which I of course
can't get right.  Can anyone tell me what's going on?  BTW, I even tried
zeroing the entire volume from the Apple Advanced Disk utility on my IIGS!