Enabling shared deploy key does not make it writable by default in 10.4

I have plenty of projects which share single deployment key.

Prior to 10.4 I was able to navigate to project settings -> repository -> deploy keys and simply click "Enable" on my shared key and it gives me writable access to the repo.

After recent update to 10.4 I was banging my head for quite some time after enabling that key for a new project (as I used to do). Only after clicking "Edit" I've got to know, that newly activated deploy key is not writable any more and I have to check the checkbox for that.

Please tell me, if it is by design now and explicit action required to enable write permission after activating a shared key?

Changelog for 10.4.0 (2018-01-22) has one record about that: Fix writable shared deploy keys.

But it is not clear, what exactly got fixed.
Unfortunately, I haven't found any glue in the documentation either.

Also, if new behaviour is "read only deploy key", could it be any global setting to revert it back as it was before?

Any comments would be highly appreciated.