Vectors filling in when PDF imported on some files? Convert to EPS and all fine?

Processing several pdf files a day for output to a RIP for plate making. 95% pull into Corel fine and reproduce as displayed on PDF format. Every now and then when the pdf is imported into corel some vectors fill in and are reproduced in the film. Convert the pdf to and eps and then import and it works fine? Can anyone help? Is this a setting i need to adjust in Corel. I can attached the latest file to have this issue if it helps, but it is 1.32 Mb.

Thanks