Hmm.. weird. Haven't seen that. Looks like the volume level is stored in the winamp.ini file with volume=##. For me it's volume=206 which is apparently 80% (I changed it in the player and this value changed) . Suppose you could do a comparison of that value pre and post update to see if it's changing.
I agree, it's weird and has only happened with the last few releases. I always shut down WACUP and make a copy of the contents of my WACUP's user folder before installing a new release. I'll start doing a pre and post update comparison of that value in winamp.ini.
I leave the internal volume level at 100% (255) in my ui configurations for all of the skins I use and use the volume control for my speaker system to control the final output level I hear. Therefore, I never use any of the in-app volume controls during playback. I have enabled the WACUP option to prevent the mouse wheel from altering the volume. I also have enabled the option to use output plug-in specific volume control instead of OS only control. I have the OS process volume set at 95%, so the effective volume level is 95%.
The value in the winamp.ini copy I saved before installing build #22222 (x86) is 251. No idea how that happened during the last shutdown before the update. So it wasn't the installer, the value was somehow changed in winamp.ini before the installation.
I've an app called WinDiff that has been in my tool bag for years. I use it to flag differences in text files, among other things. The only relevant difference between the winamp.ini copy and my current winamp.ini file is the volume value.