AMD released its Catalyst 15.9 beta drivers earlier today. While beta drivers are usually smooth sailing, this was not the case with this release, which contained a memory leak bug. According to the aptly named Reddit user "MemoryLeakBug", it triggers when resizing any window, at which point RAM usage skyrockets to about 1GB per few seconds of resizing.

"AMDJoe" confirmed the issue and says a fix is in the works. In the meantime, roll back to an earlier set of drivers while you wait on a new release. That or just don't resize any windows...