[BUG]Datepicker displayed value is not updating correctly

Hi ! First of all thanks for the amazing work.

I just updated bokeh to 1.3.0 and noticed that the displayed DatePicker value is not updating correctly after changing it manually. Basically, the underlying value responds well but the displayed value corresponds to the selected day - 1 day. So if you click on 30th July 2019, the displayed value is 29th July 2019. The displayed value updates correctly only if you select the 30th July a 2nd time.

I just checked with 1.2.0 and we don’t seem to have this issue (tested on chrome, Edge and firefox).

Minimal Example code:

from bokeh.models import DatePicker
from bokeh.io import curdoc
import datetime

def callback(attr, old, new):
    print('old:', old, 'new:', new)

date_picker = DatePicker(value=datetime.date.today())

date_picker.on_change('value', callback)

curdoc().add_root(date_picker)

Thanks and sorry if it’s not the right way to submit an issue, it’s my first time doing this.

Software version info: Bokeh - 1.3.0 Python - 3.7.3 Chrome - 75.0.3770.142

[madkopp]

If you can help me get set up I’d be happy to help test.

[bryevdv]

NOTE: #9509 re-fixes this and many other datepicker issues (as well as adds selenium tests) for 2.0 but note that the implementation was switched to Flatpickr, and also now date values can only be expressed as ISO date strings, or datetime.date and nothing else (in particular no more datetime values which caused endless trouble with time zones)