If I let Wikipedia evaluate expression {{ #expr:1000000 }}, it sometimes shows 1000000, but sometimes 1.0E+6. The change happens only when the page is regenerated. I think it is beacause WP uses both 32- and 64-bit servers and they generate different results, like in this bugreport:
http://bugzilla.wikipedia.org/show_bug.cgi?id=6356
You can try it here: http://en.wikipedia.org/wiki/User:Svick/Sandbox?action=purge
This isn't just cosmetic, because some WP templates expect the correct value (without 'E').

Version: unspecified
Severity: normal