Ok, I feel bad now, it's the second time I was wrong in this post.
This is a bug, but I swear it wasn't happening yesterday! Your project must have infected my NWJS with this bug :)
I reported it on Scirra bug tracker:
No Problem sensei, as I said I'm always learning from you and I appreciate it!
I'm actually glad it's a bug because it means the code is fine (in that department at least)
Thanks for reporting, I hope it will get fixed because it is a weird one that users will notice sooner or later anyway.
To work around this bug - after opening the dialog you can deactivate the group with "On LoadButton clicked" event, and when dialog is closed/cancelled, wait 0.5 seconds before re-activating the group.
As I mentioned before, I tried this with 0.25 (which is enough) but the problem is, not sure if you remember when I Enable one group I Disable other group (Load / Import) which are sub-groups in a main EXPORT IMPORT group and it's so much complex and tricky to do that in my case now (I tried all day long hehe) also there is a SAVE LOAD group that holds the sub-groups of Save and Load (separate groups) and if I disable these... the moment I enable it back (after the wait is finished) on cancel, both the Enable / Disable options are ON or OFF together so it makes the One OFF vs ON to BOTH ON or OFF so it makes my specific code a messy and of course the "bug" won't be solved completely that way.
In other words, this solution is a messy one for my current project so I hope it will get fixed in a more "natural" way either than expanding the code manually inside each group (because I have no other choice as I explained).
Thanks for exploring this, I really hope it's something that will be fixed soon so we can give it a try and see how more natural things will work with the NWJS dialog window.
Still... I don't understand why we're not having a simple: "Ignore Mouse Input" (or Keyboard/Joypad) as a general built-in event/action, it's a very basic need that could help not just in this case but in so many other cases.
I wish we had it but from my experience, asking for features is always denied with the same answer of "not needed" and show a very longer way to do things to walk around so I don't even bother suggesting this feature.
Just imagine how simple things would be with such built-in function in C3 ! (I would use it a lot, especially for game projects)