I was going to make an entire post about this and still may. As far as I can tell there is a minimum distance before RTH really works. I have noticed exactly what you have but I am not sure what the distance was. I was wondering if the programming logic was such that if the drone was less than a certain distance away either it was in a circular distance of error or that if you needed RTH at 40 feet your needs are beyond that which the software can provide.
I was planning on doing a series of test flights to test this for the actual distance tonight but the weather is uncooperative. I do know that once I do exceed the required distance RTH has worked quite well.
Had a feeling something like this would be the answer, just dont have time to test at the moment. Next call was going to be to Parrot to see what they say, but would be great if you had time to do testing and publish your findings, might save other behind us wondering.
Thanks