This is due to a change in the logic of when Color Management is applied. In the Alpha Release, when you enabled LokDev, the View Transform (Filmic) was ignored entirely (and sRGB / Default used instead), unless you had the “use scene lights” checkbox in the LookDev popover enabled. This was utterly confusing, as sometimes you would have Color Management doing its job, sometimes not, even though it was always configured as on in the interface.
Now Color Management is consistently always applied in LookDev mode, and this is the desired behavior. So you can consider that in this case the Alpha release was considered to have a bug.
See this bug report for reference.