The first thing that bugs me about JT-65A and especially the program is how slowly it decodes. Often you've got about two seconds after a decode to click in the response - not nearly enough time.
Other problems: Some stations go straight from signal report to 73 - why no RRR? The station that sends the signal report over and over. If he hasn't decoded tell me. If I click too late the program sends the message I didn't want to send.
The JT-65A program often does not decode and begins again only when I reboot my computer. When it doesn't decode the Raw Decoder often says ' a too weak or strong signal'. How can the program decode seriously weak signal such as DX in that case? My experience with JT-65A mode is it does not live up to it's expectations. You should be able to work DX stations world wide if the program decodes to -25db as it is supposed to. From Florida I rarely hear VK or JA stations with a vertical or directional wire antennas. So calling it a 'Weak Signal mode' seems an exaggeration in my opinion.
I wonder if you slowness in decode is related to your equipment. When I first started using this mode I was running an inexpensive machine that used an ATOM CPU. Running the WSJT suite it seemed "a bit" slow until I tried using WSPR. It would take up to 30 (or more) seconds to decode WSPR data. When I switched to a somewhat faster CPU (or course anything is faster than the ATOM chip) decodes were faster. If you use the WSJT suite for JT-65 you have a choice of decode settings, including "quick decode" which even helped speed up decoding with the ATOM chip.
Stations will sometimes bypass the "RRR" message. Especially DX stations that are trying to run as many Q's as possible. If they go past RRR to something like 73 it implies that they received your "R -08" report. If they had not received your R-signal report they would resend your signal report (i.e. the second message).
For what it's worth I have very average equipment and a single vertical antenna. My first two JT-65 QSO's were HI and Asiatic Russia, running 5 W. It will decode below -20 dB consistantly and my major reason for using it is (was) that I do a lot of QRP operating. I made a bunch of stateside contacts running 2 watts and less. The JT-65 portion of the band has become a bit congested so I have migrated to JT-9 which makes very efficient use of bandwidth. Just put KH6SAT in the log last night on 20 meters @ 5 watts.
Good luck & 73 Doc WB0FDJ