Your launcher has decided to be extra thorough with this update. If it exceeds 400% it's possible that you will be jettisoned into the future.
Joking aside, this generally occurs if your game client was a few builds behind when you updated. The status bar tends to make sense when you're either up to date or one build behind, but can display like this if you're multiple builds out. While it may extend further during the installation, everything will install and patch normally so it's not a cause for concern.
Thanks for reporting this. If you're reading this from the future, assuming the internet as we know it is still available, let us know what it's like!