Issue in PDF export from InDesign CS4

Hi,

We are facing one issue while creating  PDF file from the InDesign document. The document has 2-column texts created in InDesign CS4 application.

The issue is, we export the PDF from InDesign document. When we open the PDF in Acrobat and selecting the text (using selection tool), the second column text is selected first and then it selects the first column text. So while copying the content from the PDF, it comes is reverse order (that is Second column text, then first column text).

Could anyone suggest me how to solve this issues.  Is this bug in ID CS4?

Thanks,

Gopal