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0011205Dwarf FortressDwarf Mode -- Transport/Haulingpublic2020-01-09 02:592020-01-11 03:11
0011205: Tiles on top of constructed walls are marked permanently impassible where trees have been cut down
After constructing buildings on the surface, tree branches block passage along the surface of the wall. After cutting down the tree, sometimes the wall top tiles are still impassible.
Build a long wall among large trees. Build access at one end of the wall. Observe that branches of trees block access to the far end of the wall. Cut down trees. Attempt to build a construction at the far end of the wall.

Expected behavior: the construction is completed.
Observed behavior: the construction cannot be built because there is no access to building material. Alternately, the construction can be designated, but the only building materials available are logs from the cut trees. The construction job is never accepted in that case because there is no access to the site.
I have never been able to verify that this is fully repeatable, but I have a save that I reproduced it with, which was created using a copy of the LNP I downloaded earlier this week. This fresh copy has no mods except increasing the value of honeybee products. I have been seeing this problem since October 2018, in my last megaproject fort (which had a few, entirely different mods, mostly with clothing).
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Issue History
2020-01-09 02:59doublestrafeNew Issue
2020-01-09 03:14doublestrafeNote Added: 0039659
2020-01-11 03:11PatrikLundellNote Added: 0039663

2020-01-09 03:14   
After saving the file to make a copy and reloading the save, the specific place I saw the behavior had disappeared. This may be a workaround in some cases.

I had three constructed wall tiles (W) with constructed ramps (R) to the north, like so:


I had previously cut down a tree that was overlapping the wall. I was attempting to build a bridge to the south. If I tried to designate a 1 x 1 bridge at the tiles marked 1 or 3, I could build it successfully. At position 2, construction was blocked. There was nothing else to explain the blockage. The center wall tile was impassible.
2020-01-11 03:11   
Every time I've encountered this bug save/reload has worked around it (and I thought it had been reported long ago, but my attempt to search for such reports failed now [although bug tracker searches fail more often than not for me]).