I am using 12.12 under ubuntu and found some issues (prusa mendel i2)
1. the project planner will not place multiple objects correctly.
to recreate place 4x
12.12 - it will try to line them up in one row in the center of the bed (incorrect)
12.10 - it will place them in a 2 rows of 2 (correct)
2. the project planner does not auto center some parts
12.12 - tends towards the left edge of bed
12.10 - centered