E+Card - renewal

Just out of curiosity and on the off chance that someone knows the legal ins and out: I am holder of a E+ card ("Document ter staving van duurzaam verblijf") which I understood to mean that I have the right to stay in Belgium indefinitely as a EU citizen who has lived here for ages. I applied for renewal recently but since it had expired more than 3 months ago I had to submit proof of earnings and sickness insurance first and I am still waiting to hear whether my salary slips will be accepted as proof. Is this legally correct - that E+ cards are not automatically renewed in such a case?