To reproduce:
1. Create new project
2. Add new game object to the hierarchy
3. Add WheelJoint2D component to the game object
4. Set Suspension angle to any big number (for example 1000)
5. Create two prefabs from that game object
6. Go to Edit -> Project Settings -> Editor
7. Set "Asset Serialization" mode to "Force Text"

Actual result: first prefab Suspension angle changed to 0 (or other small number)

Note: open prefab in text editor and notice that Suspension angle has correct value (1000)

Regression introduced in 5.3