Originally Posted by nrapallo
How this "bug" can persist is beyond comprehension!
Unfortunately, the standard allows this behaviour, which is one of the differences between OPS and XHTML/CSS. The standard reads "Reading Systems may set the value of any margin property whose specified value is auto to 0." See footnote 1 in section 3.3
You can get around it by putting your content inside a table block that has been centred. See this thread
for some work-arounds.