Thanks for the reply.
For your kind information, flashplugin-nonfree come as a part of ubuntu-restricted-extras which is not installed by default as this is a non-free plugin. When you try to play a media which requires non-free plugin, you are intimated of the same and you may wish to install it or not as per your choice. If you agree to get this non-free plugin installed, it installs the plugin for you.
Yes, Pulseaudio is known to have problems when the flashplugin-nonfree is also installed. Hence the general suggestion is to use ALSA or ESD as the sound server. What we would like to confirm is, when you filed this bug where you using Pulseaudio or ALSA? Can you also confirm that the bug doesn't occur when ALSA is chosen? Thanks in advance.