Issue with date fields and DST

Hello,

I'm using a date field in one of my templates. Everything seems to work fine on my development machine.

However, when I deploy the module to an Azure hosted app service, items with a date during British Summer Time are stored as 23:00 the previous day.

e.g. I set 10/05/2018 (10th May 2018) in the edit UI. But {{EventDate}}`` renders as 2018-05-09T23:00:00+00:00(which is 9th May 2018, 11pm). "Edit Raw Data" shows the same thing in the JSON:"EventDate": "2018-05-09T23:00:00+00:00",`.

The same symptom is repeated in the "publishstartdate" and "publishenddate" fields.

Dates set outside BST are correct (e.g. 22nd November is correctly stored as "2018-11-22T00:00:00+00:00").

Have you seen this before, and do you have any idea how I might fix it?

Thanks,
Olly.