[development] module_preprocess_hook not always called

[Matt Connolly]

Is there a reason why a module's preprocess function is not always  
called?

I have several preprocess functions in a module, and I'd like to  
preprocess certain pieces of themed content based on content types  
specific to this module - so, it makes sense to me that the preprocess  
code should be in the module file.

I've traced through the theme() call, and my module's preprocess  
function name appears in the $hooks array.

For example, i'd like to hilight a menu, so I'm trying to preprocess  
theme(links).

My theme has a theme_links function which generates the html output,  
but in this case the preprocess function is NOT called.

For other pieces of themed output, using hook.tpl.php files, the  
preprocess functions ARE called.


Is there a reason why?

-Matt