So you have a door? Really? Wow! Around here paralegals have been taken out of offices and put in cubes.
I've seen law firms do this to people - string them along as temps. I've talked to these folks, they don't understand and I would love to tell them, "If they wanted you perm, they would hire you perm." Yeah, HR talks and other employees may know that they have no intention of converting you. I always knew, but could never tell. Temps are never treated very well, you know. Do you read the Dilbert comics?
It may not be anything personal to you. They may think that paralegal on family leave may eventually come back or they may be wondering if the work load is heavy enough to have a perm paralegal. They may not be sure you are a match for the job. They may just be enjoying the savings of having you as a temp and will drag it on as long as you let them.
Even if they convert you to perm at this point, I am not so sure I would want to be a perm there if I were you. You'll always be behind the 8 Ball.
I would look for a new job while hanging on to this one. Staying at this one long-term is just going to do a number to your confidence level. Since you're a temp you can take advantage of that and miss work for interviews.