When building a fire pole over a ladder segment you can't deconstruct the ladder while the plan is in place, even though the ladder segment doesn't look like it's going to override the ladder.
Pressing deconstruct does nothing but highlight the deconstruct button briefly.
- Build 1 ladder segment (Sedimentary Rock in this example)
- Send a build order for a fire pole (Cobalt in this example) over the ladder.
- Before the fire pole is built, try to deconstruct the ladder.