From the tags page of an entity I can add a new tag. When I click add tags, the tags I've written are added to the list above.
If a tag has upper-case letters, it is added directly to this list. Then, a few moments later, the tag appears a second time in lower-case. Refreshing the page leads to the upper-case tag disappearing.
My guess is that the change gets made to the table before an ajax submit/refresh, which causes the lower-casing to happen and get added to the table as well since it's a 'new tag'