You seem to fail to comprehend that you have *TWO* entirely separate MDB databses defined in your configuration. You set the maxsize on one of them, you did not set the max size on the other. That's why <something> is attempting to resize your database. You'll have to track down what's attempting to do that resize, because it's not OpenLDAP. But the thing you really need to do is fix your configuration so both databases have a maxsize configured.
Oh. Now I see. It's true, I have selected mdb backend for log database too, and as you said, maxsize for this database is not explicitly set and therefore slpad is using the default value which is not enough. I will correct this and see if the error stops. That totally makes sense, but only now I got it.
Thank you so much.