TLDR: This bug (or feature?) is actually triggered from the overall weight of you and your watercraft, and where/ how you enter the ice. if you want to use watercraft across ice and water, use punt instead.
Did some tests in 2 weeks before midwinter, here are the result.
1. Ice will break when items laying on it weight over 4-5 tree trunks (safe at 2000 lbs and break at 2500 lbs).
2. However, Human with raft (around 1250 lbs) are enough to break the ice from if you enter the ice from water.
3. If you push raft from shore into ice surface then walk to that tile of ice, although the total weight do not change (1250 lbs), the ice only make cracking sound and you can safely walk away.
4. Human with punt (around 120 lbs) wont break the ice no matter you enter the ice from water or carry it walking across the ice.
5. Human with punt and 2 tree trunks (around 1120 lbs) will break the ice if you enter from water.
6. Human with punt, 20 stones and a tree trunk (around 860 lbs) wont break the ice.
7. Human with punt, 30 stones and a tree trunk (around 1000 lbs) will break the ice.
So the conclusion is, dont use raft in winter and even if you have to carry a large prey across sea and frozen water, a punt will have no problem. Just bear in mind the ice wont hold the weight of multiple large preys even if you use punt.