I searched the forum for this and found the exact same issue, so I know it's not just me...  However, there was no resolution to the issue, so here I am.  When I select more than one track to normalize, the resulting Edit(n) edited wavefile has a W64 extension, and is a combination of the files that made up the selected tracks.  I discovered this when waveforms failed to redraw, even after clearing the picture cache.  The project is pretty big, about 2.5 hours, but I don't know if that has anything to do with it. 
 
I am using X1 build 425.  I have X2, but it seems that X1 is more stable on XP (SP3), and I'm not ready to rebuild a work station that's been configured to my liking over many years.
 
I really need some help on this, as I had no control over the levels I got from the FOH guy, and most of the 48 tracks x 3 days of concerts are low.  I normalize so my compressors, etc standard settings work pretty much the same across various material.  Don't want to argue this point...
 
Thanks.

What version of X1?
 
X1 was hopeless on my system until about x1e, if I remember correctly

Hey Jonesey,
 
I looked in the Help/About, and the only version identifier is the build number (425), but I don't think it is specific to a version, as the other entry in the forum was for another version altogether.

Update... As I am splitting this project up into 1 song per project projects, I noticed that selecting multiple tracks to normalize still combines them, but the file extension is .wav.  Still does not explain why they are being combined, but I think the W64 extension is being added when the resulting file is very large.

Another update.  It does this in X2 as well.

FWIW, I tried several ways with 2 and 3 tracks but could not duplicate this with X3e

Anyone else?

I could repro with X2, so presumably is an issue with X1 as well. I never realized that "mass normalization" created a new WAV, but did notice that when normalizing multiple tracks, the gain would only increase as much as the highest track would allow - in other words, if one track peaked at -6 and another at -3 and I normalized to -1, they would peak at -4 and -1 respectively. Your experience explains why. As a result, i got into the habit of normalizing individual tracks because normalization doesn't do what you want it to do with multiple tracks, so it sounds like that's what you'll need to do.
 
Incidentally if you normalize any track in X2, it will create a duplicate edited version. Because this is a destructive process, SONAR has to create a separate temp file in case you want to undo. However because it's a temp file, if you "save as" and specify one file per clip, the temp files go away.
 
Haven't tried with X3 but will later today.

In my humble opinion you would never Normalize multiple tracks anyway. As what Craig just said. If the goal is that all your audio tracks at say -6Db then each track will need treatment. 
I Tool copy into wave lab to do this action as I find Sonars Normalizing is working blind.
Your better off just using the Gain if  track is low.  

johnnyV
I find Sonars Normalizing is working blind.

Can you elaborate? I don't understand what you mean, but it sounds interesting