RSX-11Mplus boot SAV -- Cannot find Home Block on fpga pdp2011

I've long thought that my pdp2011 would run just about anything pdp11. However, it was recently brought to my attention that RSX-11Mplus will not boot from an rp06 disk image. I mean, an rp06 image created on simh, based on the rd54 image in rsx11mpbl87.dsk.bz2, sysgenned to support rp06 drives, and working without any problem on simh. The first steps in the boot on the fpga appear to work fine - several reads are done, and the first message appears: "RSX-11M-PLUS V4.6 BL87 1024.KW System:"RSXMPL". So far exactly the same as when I run simh on the same image. However, after a brief pause in which the cpu is busy, a difference appears: simh will continue with a few reads and finish the boot process; however, my fpga will start reading sectors from each cylinder of the disk in ascending order - ie, beginning at cyl 0 and ending at the last one. When at the last cylinder, the message "SAV -- Cannot find Home Block" appears. Strangely, if I google that, it comes up with a reference to Ersatz-11 from 1994 which appears to describe exactly the same behaviour - only then on RL, apparently. See ftp://minnie.tuhs.org/pub/PDP-11/Sims/Ersatz-1.1beta/Old/e11beta.txt I've spent most of my free time last week chewing on this problem, looking at many details in my controller vhdl. However, I've not come any closer to a solution. At this point, I'm not even completely sure that the problem actually is in the controller - since E11 had the same thing in it's RL, and that is a completely different thing. So, I'm hoping that someone on this list can help me understand what the trigger(s) for the "SAV -- Cannot find Home Block" could be. Is there maybe someone who remembers the original issue in E11, and how it was fixed? Or is there someone with access to the source code who could explain what happens?