kPDEPath that 'hide' text

Hello,

I have two kPDEPath, and some text elements 'overlapped' to these Paths.

One kPDEPath hide the corresponding text, the other Path does not hide the text. If I remove the first Path, I can see the hidden text element in the PDF.

My question is: why the two paths bheave in different ways? They have the same PaintOp (2) and GState values.

How can I determine if one path 'hide' some text or not?

Thank you