I imagine you would know best whether to trust the animation studio or not, especially if you have been dealing with them since 1999.
When attending the meeting with the production company and your studio on Monday, where the issue of you writing the script will be discussed, find out what terms are being offered.
If presented with a contract of any kind, do not sign it until you have the opportunity to review it carefully.
After a review, if you do not feel your best interests are being represented, or if you have
doubts that your best interests are being represented, it would be wise to talk to an attorney.
Contracts are only valid when both parties to the contract agree on the terms. Everything is negotiable. Of course you want to negotiate for the terms that are best for you - but be sure to take into consideration the role the animation studio plays in your financial life. It may not be in your best interests, for instance, to get excellent terms for writing the script only to lose a primary source of income with the animation studio.
So to answer your question, "Do I have reason for concern?" the answer is that if you are concerned, there is probably a reason to check it out with an attorney.
