Newline being inserted after plugin

I created a smarty function called {link_to_template} that creates a
URL designed to go inside a <a href=""> - for example:

<a href="{link_to_template param1=xyz}">Blah</a>

This creates a cache php file with the following:

<a href="<?php echo
smarty_function_link_to_template(array('param1' =>
'xyz'), $this);?> 

">Blah</a>

There is a single blank line after the ?> (not two in the code above,
I inserted one for readability).  This was never a problem under
php4 - but moving the same site to php5 I get an error now:

Fatal error: Cannot use string offset as an array in ...

I verified the actual return value in the plugin does NOT contain a
newline so it seems smarty is putting it in there.

Is there any way to prevent a plugin from automagically inserting a
carriage return after the ?> or is there something else I did?

Thanks,

Josh