I am not completely sure about the cause, but I have come by a strange behaviour by some templates (e.g. http://commons.wikimedia.org/w/index.php?title=Image:Policarpa_Salavarrieta_2_pesos_Oro.jpg&oldid=8606384). After a bit of playing, I was able to create a quite simple reproducible test case (see the URL at this bug report):
- a template uses some parameters without default values
- you make a call to the template, with some parameters not defined
- and you wrap the call to some {{#if:}}, even with a constant condition
The result: strangely broken rendering.
(I am not sure if the bug is in the parser proper, or in the ParserFunctions.)
Version: unspecified
Severity: normal
URL: http://test.wikipedia.org/wiki/TemplateParametersBug