Yes, you are right.
I found the cause of the problem. The curprit was loading v1.43's queue to v2.0.
I uninstalled v1.43 and deleted FlashFXP folder.
I installed v2.0. No more queue files.
I connected to the same PUB and put files in queue and started downloading.
I disconnected from the PUB. (I did it for test.)
I reconnected the PUB using queue.
It has been working flawlessly for several hours without any QUIT command since I reconnected.
No more QUIT command after completing each files nor QUIT command after PWD.
I suspected loading old queue files once but dismissed it. Because v1.43 worked flawlessly with v2.0's queue files. So why v2.0 not working with v1.4's queue files? Even v1.43 has a good forwards compatibility.
Thanks a lot bigstar!
You have the best Tech Support.
I'm a happy camper now.
Regards,
petrus