Industrial Toys - studying your note again. What I had thought of was ordinary leak-down back through the valve. Hadn't occurred to me that the problem could come the other way also through unwanted pressure. Do you think this item would be a fix:
1/4" NPT 6 GPM CHECK VALVE 5 PSI CRACKING
Just to wrap up. I have used it for 5-6 weeks. The locking pins sometimes loosen a bit overnight, I make it a habit to give them a push when starting up. I might add a plate to provide more protection for the valve fittings and hoses. Can't think of any other issues.
Grapple plumbing is complete, that is what I am working on now.
A holding valve would fix this if it's a big deal, no?