Strange hyperref Info in log file

What could be the source of the following message contained in my log file?

Package hyperref Info: bookmark level for unknown unnumbered defaults to 0 on input line 48.

I should say that input line 48 and the lines before and after it only contain text, formulas and a blank line. There is a labelled equation environment but if I delete this, the message is still there (the label is the only thing which could possibly be connected with hyperref). I cannot reproduce the message if I compile these lines alone.

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Can you provide an MWE? Code to reproduce the issue would be very helpful. –  AstroPig7 Aug 14 '12 at 16:47
Well, as I said, I tried but failed to reproduce the issue in an MWE. –  lpdbw Aug 14 '12 at 18:22