Odd, erratic warnings

I've seen several instances of odd and unrepeatable errors from the 
validator recently. Out of the blue a warning will be returned that 
says: "This property applies to block-level elements".

Do nothing to the page and resubmit it to the validator and the 
warning disappears.

I've attached two pdf files. The first (blocklevel_Warning1.pdf) 
shows the validator results page displaying the warning, the second 
(blocklevel_Warning2.pdf) is the result of the same page (with no 
alterations) resubmitted to the validator.

Any ideas what is causing this?

Be aware that this file is not my own - I'm marking students work at 
the moment and I've encountered this error with a number of different 
students' files. I have never encountered the issue with my own css.

Regards,
Morag
-- 
_______________________________

Morag McKenzie

Comp112 Teaching Fellow
Department of Computer Science
University of Otago
Dunedin, New Zealand        

Room 2.10b, Science 1
Phone:  (03) 479 5242
Email: morag@cs.otago.ac.nz
_______________________________