Well flash in general has been known to be problematic in linux, so I had to ask.
Opera and flash in linux did have some issues last time I used opera, thus was part of my motivation to use chrome instead.
If you have more issues with opera I cannot help much in that area, I really dont use opera nor care to at this time.
Opera is pretty much dead to me, if you like it more then other browsers more power to you.
The main star browser in linux right now is Google chrome, sure its not perfect but it does offer its own flash wrapper.
But that wont be for much longer, firefox is developing their own flash alternative.
If you want to install normal flash i suggest you get it via the repositories in Muon, there is a metapackage called Kubuntu restricted extras which will not only install flash but most other codecs you may want.
The only thing it wont do is pull in DVD playback, that you will have to install something called libdvdcss which can be found here:
http://download.videolan.org/pub/debian/stable/