template string replacement not working

[h2ojunkie]

For some reason I can't seem to get this string replacement to work, and I thing it has something to do with the $session part of the string

This doesn't work:

$vbulletin->templatecache['threadbit'] = str_replace('showthread.php?$session[sessionurl]t=$thread[threadid]$thread[highlight]','SOME REPLACMENT URL',$vbulletin->templatecache['threadbit']);

But this works:

$vbulletin->templatecache['threadbit'] = str_replace('showthread.php?','SOME REPLACMENT URL',$vbulletin->templatecache['threadbit']);

And this works:

$vbulletin->templatecache['threadbit'] = str_replace('t=$thread[threadid]$thread[highlight]','SOME REPLACMENT URL',$vbulletin->templatecache['threadbit']);

Any idea why the str_replace doesn't work if $session is in the searched for text?

Thanks