The current task pane "hard-codes" the initial url given with a set of predefined parameters.
So given a url of "/foo/bar.php", the resulting url is:
/foo/bar.php?SESSION=someuglylongsessionid&WEBLAYOUT=Library://Path/To/The.WebLayout&DWF=0&LOCALE=en
But say I want to supply a url with parameters "/foo/bar.php?snafu=0", I will get the following url:
/foo/bar.php?snafu=0?SESSION=someuglylongsessionid&WEBLAYOUT=Library://Path/To/The.WebLayout&DWF=0&LOCALE=en
Note the two "?" characters in the query string. Thus passing in an initial url with additional GET parameters, will trip up any page in the task pane that is expecting these additional GET parameters.
