From the
wiki:
Items can occasionally be left inside a wheelbarrow, causing the wheelbarrow to become unusable. This can cause a stockpile to stop collecting items if all of its wheelbarrows end up in this state (Bug 6074) You can work around this by marking the contents of the wheelbarrow for dumping.
If
this is the bug report you're referring to, you might want to contact Footkerchief or Dwarfu to get the report re-opened.
Edit: I can confirm that an interrupted hauling job leaves items behind in wheelbarrows, and those items aren't removed upon arriving at a stockpile. However, I haven't been able to make the wheelbarrows unusable - dwarves will still use the wheelbarrows for hauling if they already contain items (even forbidden items).
Edit 2: Can you check to make sure the wheelbarrow(s) aren't forbidden? (When I tested this, it appeared to make the stockpile tile the wheelbarrow was on unusable temporarily, although freeing up other tiles triggered more hauling jobs with a new wheelbarrow.) Is there anything else unusual about these wheelbarrows (e.g. melt-designated, not fortress-produced)?