pert:
I haven't ever shipped palettes but I frequently receive them and that's actually where I see the worst breakage. I think the culprit is the forklifts.
Packing !
At 5 ft long excessive packing could cause this. I am assuming you are using euro 2 pallets for this.
With long glass tubes if there is too much cushioning the bending moment can cause breakage with a big drop off a forklift.
No definitive data though.