Text disappeared after Acrobat preflight

Hi all,

A few days ago I preflighted a PDF using the 'Convert to PDF/X-1a (Coated FOGRA39)' preflight profile in Acrobat X. After preflighting and optimization several pieces of text suddenly disappeared. I'm a bit puzzled here. Customers of me are using this preflight profile to optimize quite some PDF's in their workflow for print production. Has anyone experienced similar kind of problems with this profile (or another in Acrobat preflight)?

I ran my tests on Windows 7, Acrobat 10.0.1.

PDF A, before preflighting

PDF A, after preflighting

PDF B, before preflighting

PDF B, after preflighting

All help is welcome.