TDG-V0.0.25 for V5.0 states for the equation element:
[Processing systems that number equations or build a table of equations at the beginning of a document may have difficulty correctly formatting documents that contain both equations with titles and equations without titles. You are advised to use informalequation for equations without titles.]
Assuming this caveat doesn't say that such...
2009-10-31 02:47:37 UTC in DocBook