Highrez

XMBC Version: 2.19.2
Installed or Portable version: Installed
Windows Version: 10 with latest updates
Mouse Information (brand/model): Kensington Trackball Pro
Relevant Computer Information (CPU, RAM etc): i7 8700k, 32GB
Did the problem occur after an upgrade of XMBC? (If so, from what version?): no
Did the problem occur after a Windows update/upgrade? (If so, from what version?): no
How long have you used XMBC?: a week
What language and keyboard layout do you use in Windows?: International English layout

Clear description of the problem - try and include as much information as possible, including what button and mappings you are having problems with (if applicable).:

I'm trying to use X-Mouse to program shortcuts that I often use in Avid Pro Tools to the upper left and upper right buttons on my Kensington Trackball Pro.

Simple key combinations with one modifier key work normally, such as:
Ctrl A
Ctrl S
Ctrl =

HOWEVER, more complex key combinations don't work, such as:
Win Alt Shift \ (new playlist for selected tracks)
Shift Alt Up Arrow (copy selection to target playlist)
Alt Shift 3 (consolidate selection)

I read the manual for X-Mouse but couldn't get any insight into this problem. This problem is only in Avid Pro Tools, not in other applications. Obviously you'll say "contact Avid," and I did but they refused to help.

Do you guys have any ideas?

Here's an example of my mapping, maybe I'm using wrong syntax:
(pressed)[{LWIN}{ALT}{SHIFT}\] for Win+Alt+Shift+\

I can't see anything obviously wrong with your syntax, but can you try method 3 (during) and see if it makes any difference? It shouldn't but I'm curious!
I don't have Avid pro tools (and I'm guessing there is no free/trial version I can test with?) which makes it a little tricky to try and reproduce here.

Thank you Phil. I tried "During," but nothing changed.

There was a free version of Pro Tools but that changed as of last week...

Pro Tools has a very strange behaviour with the Alt key. If I use Alt + Tab to switch from PT to another program, next time I go into PT, the Alt modifier key won't work for anything - unless I tap it twice - then I can use it for a shortcut command again. Otherwise it just won't respond at all, not for anything. This is only on Windows, not on Mac. I contacted Avid, the manufacturer of PT, and they wouldn't help with this either. But I guess there could be a connection between these two problems. If only I could figure it out.