When you export a file to PDF for prepress the CYMK values do not stay correct. Try a spot color and check values in Corel, export to PDF prepress. Open in Photoshop or Paint and check values. They are no longer correct!! This works fine in X4 and makes X5 pretty useless for commercial printing.
By default X5 uses LAB color space for alternative spot colors definition. I.e. LAB color values are used to render spot color correctly when there is no real spot ink on the device. The LAB representation of spot colors is recommended by Pantone. X4 was using CMYK palette numbers for spot colors definition which produced less accurate colors. Still, if your workflow really requires precise CMYK numbers for spots you can go to Tools/Color Management/Default settings dialog and change "Spot color definition" control to CMYK.
Gennady