Preview reencoding/destroying PDFs

Hello,

I've the following question:

I use Abbyy Fine Reader Pro for Mac to OCR PDF files (books and papers). When I open the very accurately OCRed and compactly compressed files with preview and add highlights or annotations, Preview triples the size of the file when saving, and completely destroys the OCRed text.

Here's an example:

Before saving, the file has 8,4MB, PDF Producer is FineReader OCR Pro, and most importantly the text is identical with the text in the image.

After saving the file with this highlight and reopening it, it looks like this:

Size hast grown to 26,4MB, PDF Producer now is Mac OS X Quartz PDFContext, and most importantly the text is complete nonsense, which makes the whole OCR worthless.

Does anybody know how to avoid this situation?