I’ve done some checking and this error still seems to be there when using versions 5.32.00 and 5.34.05.
I’ve also found an topic on this forum from 2011 [url]Wrong PDF projection when using plotOn with RooSimultaneous which seems to be about the same problem but when using either the RooSimPDFBuilder or the RooSimWSTool that I used. So it looks like either I’m making the same mistake, or somehow the plotOn() function doesn’t work correctly when called on simultaneous PDFs created by these tools. I’ve confirmed that the simultaneous PDF and the subsequent PDFs and parameters are definitely in the RooWorkspace before fitting/plotting.