Opera 45.0.2552.453 Beta
fixes video play memory leak.
I have found in the past that just playing an hour of video I could easily end up with 1/4 GB of cache. If this is the memory leak they are referring to I am not certain. But I have installed the beta to find out.
Edit: Note that after pressing the Download Button you are given several download options. Supposedly the beta downloads, either 32 or 64 bit, have the video play memory leak fix.