We had a similar issue here recently, with list numbers and bullets disappearing in a document sent to authors. A couple, not all, were experiencing the problem. It turned out that they were using Word 2007, while the template had been newly created in 2010. Research indicated this as a recognized issue. After various tests, I found that saving the template in Word 2007 and reissuing the documents solved the problem.

Hardly a satisfactory solution -- ahem, Mirosoft! -- but we have not had the problem since then.

Best,
Ulodesk