Well Homer wandered out of SH and is in SP now and hes has stayed on task all night. Seems to have been a problem with the heights.
I had it happen in one of my games. The second time I sent him on the task he went to the Springfield waterfront and it finished. He'll also do the task at a river, so maybe if you surround him with a river before sending him on the task he'll stop there instead of going to the Heights.
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