I am not sure if this is technically a bug, as it may be the intended function, but it does seem to be inconsistent with the process with MP3 files.
Select some .WMA files and use "Analyze Volume" and wait for the process to complete.
Check the tags and they should say "Not Calculated" NOTE" that replay gain is ALSO NOT APPLIED to playback of the files.
Select the analyzed files and "Send To" "Rescan".
Files tags should now show the correct replay gain values and will be applied to the replay volume.
For me, the process works fine with MP3 files (meaning the replay gain shows in the tags and is applied upon finishing the volume analysis, without rescan), just not with WMA files. I tried several different WMA files with varying bitrates, etc., with the same result. I tried closing and reopening Musicbee, removing the files from the library and adding them back. The only thing that seems to "wake UP" the replay gain values is a rescan or something that triggers a rescan such as moving the file, etc.
Workaround is fairly simple. After Volume Analysis, select the files and "send to" "rescan".