You must use wedges, Spartite or something to prevent the mast from moving.
One of your wedges was simply not big enough or not wedge shaped enough and it fell into the cabin.
No big thing. Just remove the boot and drive in another one.
Using properly sized and shaped hardwood wedges, lubricated with some sort of adhesive and driving them home tight is a time tested method.
Spartite is a good product if you are looking at upgrading.
I would not recommend the rope and silicone method.