Saving AI to PDF files design becomes weird

[Hugo29344919bhty]

Hi, i wanna ask about my design files that becomes very weird especially in the blending part like the image shown below. But this just happen if i save the file to pdf, if i save the file to Tiff or JPEG the problem is gone. Still i want to save the file to pdf, how can i fix it? Thanks

[Ton Frederiks]

What do you use to view your files? Does it look like that in Acrobat?