... demolition.

That's what it is. I've got 10 trucks assigned to a certain storage with active dumping routes; it is their job to dump dirt to create a flat platform for me to build on, so as to avoid tying up fifty of my unassigned trucks with "no place to dump dirt" when the task is complete- and to keep such tasks from interrupting truck logistics or construction/demolition. That storage is full, there are plenty of reachable dumping sites in their assigned output towers' ranges, they should be hauling dirt over to the dumping zones. But what are they doing? Creating work for all the rest of my trucks, by snatching materials from a large deconstruction job and hauling them to the shipyard! They're disregarding their assigned work in order to CREATE work for the trucks that they are assigned explicitly to alleviate!

Reproduction steps:

1. DO have one or more structures built that you plan to demolish.
2. DO have a storage with trucks assigned to it. Doesn't matter what of, but it's more obvious if it's of an unrelated resource (ex. dirt or rock), or has import disabled. Doesn't matter if the assigned trucks have something they're supposed to be doing (ex. dumping dirt, moving it to another storage that just belts it right back, etc.) or not, but it's more obvious if they do. Doesn't matter if their truck type is prohibited from construction jobs.
3. OPTIONALLY have (other) storages set to receive the products from the demolition. The storage-assigned trucks will (correctly) disregard these storages, despite incorrectly taking the deconstruction job in the first place.
4. OPTIONALLY have un-assigned trucks of a type prohibited to participate in construction jobs, like amphibious vehicles. They will incorrectly disregard that prohibition, yet also disregard the location the materials are supposed to be shipped to, taking it exclusively to the shipyard.
5. DO NOT have enough un-assigned trucks available to fully satisfy the demolition task. This is because the trucks that are supposed to be the only ones allowed to take the job do seem to (correctly) have priority access to the job. An easy way to do this is for the demolition task to involve hundreds of solar panels or other high-component items.
6. Start the demolition! Pausing the game can make it easier to get large jobs all at once, but it won't be necessary if the task is large enough relative to the total truckforce.
7. Watch as the storage-assigned trucks disregard waiting jobs related to their storage in order to take products from the demolished building to the shipyard, never to the proper storage, even if the shipyard is on the far side of the map. Note that unassigned trucks that are prohibited from construction jobs will also do this, while the unassigned ones that are actually allowed to participate in construction jobs will deconstruct direct to the storages that the products are actually supposed to go to.

Worth note: If the storage-related jobs have a higher priority (lower number) than the deconstruction task, the storage-assigned trucks will properly favor their assigned jobs. The problem is that they should completely disregard the deconstruction task even if their storage has no jobs waiting, as it's not related to their storage, and is taking them away from their assigned duties!

Update 4.1 | v0.8.4a (b588)

Judging by a posting I saw on GitHub some time ago, this issue has been in the game for years (since at least 0.6.4d/b343), but disregarded as "WAD" because the extent of the issue wasn't clear. Well... then amphibious vehicles were added, and we got the "ban truck types from construction jobs" option explicitly to keep amphibious vehicles out of the core of the factory and out by the shore... and said vehicles actively disregard that restriction anytime you deconstruct something in the heart of the factory, significantly slowing down those same deconstruction jobs because they're slow, low-capacity, and often very far away, which makes it impractical to build any amphibious vehicles (unless they're mining-tower-assigned, I suppose, those won't participate in demolition, even if the tower is out of designations or has no excavators, but they also can't do construction), and renders the beautiful new bridges largely unuseable. It's not WAD (Works As Designed, for any non-developers that don't already know), it's a significant damper on playability- especially when playing Shattered Isles for the express purpose of forcing oneself to establish a varied railway network instead of just flattening everything into a Minecraft/Sandbox-style superflat!