Strange, I'll check it out. Can anyone else duplicate this?
Nope, not a problem between MPP and BookRotate scripts.
MPP + MCP + BookRotate + BookJackets (BookRotate versions) works without errors.
Tested with 'The Firmament' (bk_firmament; has BROctavo script attached), 'Brief History of the Empire' (bk_BriefHistoryEmpire1; has BRQuarto script attached), and 'abot's WaterLife Book' (ab01wlBook02; has custom BookRotate compatibility script attached; skill book).
Tried all iterations of picking up and dropping books with and without inventory open, 1st and 3rd person views.
Tested against the following:
* new game, both MPP + MCP + BR and MPP + MCP + BR + BJ(BR versions)
* loading saved game without updating load list after activating BookJackets-BookRotate esps
* loading saved game sync'd to load list using Wrye Mash after activating BJ-BR esps
I also had several other mods, some with books like abot's Water Life, also loaded and did not experience any script problems.
More likely a conflict between BR and some other mod, or a dirty/corrupt save.