During the last pass of the defragmentation process when the blocks are consolidated, I noticed in the PrimoCache GUI that I was getting a lot of Level-2 Writes / Reads, but as soon as I hit the Pause button for the caching operations, the last consolidating pass finished.
So the bug I experienced was that PrimoCache caused Disk Defragmentation Utility to stall at the Consolidating pass.
I can't reproduce it now that my disk is defragmented, so outside confirmation that PrimoCache is interfering with the OS's low level block relocations would be nice.
Background: I am using a 1TB WD Blue as the caching target and 30GB OCZ Vertex SSD as the Level-2 Cache Storage.

Screenshot of PrimoCache after defragmenting the disk