Corel export filter has been doing this for years and years! Its the settings when exporting that does this
IIRC, when they export as an eps or .ai file, they've checked the simulate complex filled curves or simulate outline effects, not sure which one does it. I think it also happens when fills are gradations, but don't recall.
Have the client uncheck those boxes and save as an .ai file, it will pretty much open with little or no issues at all, or sit there and weld all the pieces together. Sometimes its just easier to re-trace and clean it all up on your own though.....
Chris