Bug? Month increments every time date picker opens

This bug is so eye-catching that I thought it must be my fault, but it also reproduces in the simplest set up. Could someone verify?

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Attach a form with just a date field to both the start event and the user task. Set task’s assignment to the process initiator.

In the Task UI select the process and pick a date:

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Click Start Process, and go to your tasks:

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Note that the month has magically advanced by one.

Note I am on 6.2.0 snapshot of early Oct (e10e5a19), haven’t checked 6.2.0 final.
Update just validated on out-of-box 6.2.0, has the issue too. Opened issue #636.