Please read and follow Contributing Bug Reports. This isn't a valid bug report and won't currently be accepted as is. Specifically we require version information of the install and steps we can follow locally to reproduce the issue.

Finding version information seems non-trivial if you're not an administrator of the Phabricator installation. We appear to be running 0426ce73f0e63f1900f1cc285cfa1465ea72317e.

I came up with a reduced testcase. To reproduce, create the following task graph (the sequence of task IDs is important):

In addition to the bug I pointed out in the description, there is also an incorrect line being drawn - the violet curve extending downwards from T152 doesn't make sense and shouldn't be shown.

In T12114#207538, @chad wrote:

This isn't a valid bug report and won't currently be accepted as is.

I'm only trying to help you improve your own software - I have no personal interest in this issue being fixed. Imposing barriers on people taking a brief moment out of their day to draw your attention to bugs in your software seems counterproductive. If you choose not to accept reports of bugs that are backed up by a screenshot clearly showing the issue, then that is your loss.

For the records, Version info for that downstream instance says:
phabricator ef44831309df7b8d4b75ab653d1cd22813147c85 (Dec 16 2016)
arcanist 9c8774f9d30b921f0e4a5a10b98a7820517789a6 (Nov 10 2016)
phutil 77ace948f90c1003c2917175eb0a93c158023bdc (Nov 15 2016)

I'm only trying to help you improve your own software - I have no personal interest in this issue being fixed. Imposing barriers on people taking a brief moment out of their day to draw your attention to bugs in your software seems counterproductive. If you choose not to accept reports of bugs that are backed up by a screenshot clearly showing the issue, then that is your loss.

It's understood that you're trying to be helpful, we just have rules for what we accept into the upstream. These rules are based on years of observation and fine tuning on what helps us deliver free service and support to all users, not just a single company. So we have a very easy barrier to file bugs. Your version must be up to date and you must tell us how we can locally reproduce it. It saves us hours per ticket at the expense of 5-10 minutes to you. And then we get more time to help other users and develop Phabricator. If this is too much for you, my understanding is you can file these downstream and they'll be funnelled upstream appropriately with the needed information.

I was able to reproduce this locally -- or something close enough, at least -- by recreating the simpler graph in T12114#207542, so I have enough to move forward.