Unicode. Not only are characters added, sometimes attributes of characters are changed. As Unicode is a standard, there is a whole process before changes are finalised. One such step is the "Public review".
A recent public review is about a change to the category of 12 characters. Once this change is accepted, it will change the behaviour for these characters. Organisations that provide Unicode support in their products will have to adopt their products.
The result of all this; displaying Unicode may differ depending on the version of software implementing the standard.