I am having the same double-press issue as a lot of other users as well. I am not using Harmony, but an old XBox 360 controller to control my own HTPC software. It just sends Ctrl-button presses to my program (Ctrl-Up, Ctrl-Down, Ctrl-A, etc.) to run the GUI. For example when I have a menu up in my program and I press the down button on the remote, it moves the menu down twice, I.E. it sends two Ctrl-Down button presses (using keyboard's Ctrl-Down works fine so it is not my program, also, I have my other Flirc configured to use my LG UHD Bluray player's remote and it works fine, so the issue has to do with Flirc and the XBox 360 remote).
Anyway, I used to have this same double-press issue couple of years ago when I bought my first Flirc and back then I was able to fix the issue by setting the "Inter-key delay" to something longer than default value. This is still the "official" fix for non-harmony remotes in the Flirc's help page. Unfortunately the "Inter-key delay" option is no longer available. The "Advanced" dialog (I have Windows PC, not Mac) does not have the option any more, and running "Flirc_Util.exe settings" shows:
C:\Program Files (x86)\Flirc>flirc_util.exe settings
FW Version: v4.9.3
SKU: Flirc 2.0 [dori]
sleep detection: always enabled
noise canceler: always enabled
inter-key delay: N/A for current firmware
builtin profiles: NA
Memory Info: NA
product sku: Flirc 2.0 [dori]
Unfortunately I have updated the old Flirc to the latest firmware not knowing about this issue so I am stuck with the double-press problem.
Is there any place where I could download the last firmware (and GUI as well, I suppose...) which still supported the inter-key delay setting. Or even better, if you could re-enable it in the firmware and I could be using the latest version.
By the way, thanks a bunch for this amazing device. It was exactly what I needed when I started working on my own HTPC program!