A family of Microsoft word processing software products for creating web, email, and print documents.
OK, a bit of digging yields the following conclusion: it's a long-standing bug, supposedly fixed in the various Word 2008 updates, but not quite.
Solutions? Various mentioned in many forums:
- Install MathType and convert all equations to this format. MathType will run in demo mode for 30 days and revert to MathType Lite after that: http://www.dessci.com/en/products/mathtype%5Fmac/trial.asp.
- Open the document in Word 2004 and work there.
- Disable AutoRecover, as this seems to corrupt equations and would account for the "random" nature of the corruption (it would actually be periodic). This is a good one.
- Rebuild equations from scratch. This would fix the broken ones, but what's stopping Word from re-corrupting?
- Copy equations from old backups. This seems to work "mostly" (could be so, if the AutoRecover corruption is real).
- Save equations separately and link to them in the main document.
- Some users blame the .docx format, but does not seem likely.