Issue description
While digging out a store of compost, I noticed the excavator had moved outside the pile and was digging through a retaining wall.
Reproduction steps
Create a square of retaining walls with an entrance for excavators and trucks.
Dump 5 high with a ramp at the entrance
Stop dumping when the area in the walls is > 1/2 full but < full
Dig out the ramp with the designations only on the ramp and extending in, but not all the way
Once the excavator has finished digging out the ramp, set the mining designations to the whole area
Game version and build number
v0.7.5b (b454)
Operating system
Windows