Template filter date format "U" produces a timestamp that is off by 10-14 days

[Sean Brant]

When trying to format a date in a template with {{ mydate|date:"U" }} the timestamp is off. Attached is a test case that first created a datetime object based on now then renders that in a template with the format "U" and compares that to outputting the date in python with strftime('%s'), this test fails. The next test outputs the date with the format "Y-m-d H:i:s" and compares that to outputting the date in python with strftime(%F %T), this test passes. So it seems that only "U" is broken.

[Sean Brant]

Test case

[Karen Tracey]

We've already got #9850 reporting the docs/code mismatch here. We can use the one ticket for fixing the code, if the decision is to document this formatter and make it work properly.