Sonar 8.5.33. I've got Autosave set to 15 minutes or 50 changes but it Sonar Saves every time I stop the transport. 
I tried to get to the bottom of this issue some time ago with no success and eventually concluded that too often is better than not often enough.
But sometimes I'm on a roll, working fast, and waiting for Sonar to plod through the Save is irritating and throws me off.
Does anyone have an explanation? 
Thanks - rev

Hi. Does it happen in all projects, or just one? Do you have any automation in your project?
That could be responsible for those changes during a simple play, stop.
I'm just guessing here.
Best of luck.

Zargg: No automation is in the project and it does happen in all projects. If Autosave is working properly, the explanation must be in the definition of 'changes.'
I keep my lyrics in the Info panel found under the File menu and I've noticed that typing 50 characters will make Sonar Save. So one character is considered a change (as you would expect). 
But when I'm trying to sing and I'm not editing in any other way, it's kinda puzzling - unless 50 audio slices are considered changes. At 44k per second, I would exceed that almost instantly and trigger a Save as soon as I stopped the transport. 
That scenario doesn't seem likely though, I would expect the new clip to be considered a change.

That's strange.
Perhaps up the number of changes to 200, and lower to 5 mins save interval to see if it helps?
Hopefully someone else will chime in with more knowlegde.
All the best.

IIRC, one of the save options was bugged, but I cannot remember which (I think I remember that the time interval worked, but the number of changes did not). Try using only one or the other, but I would start with just 5 minutes and remove the # of changes completely. I am not sure if another solution had been found for this. Many of us became accustomed to simply hitting Ctrl-S every 10 minutes (or before major edits like bouncing, Audio Snap, Region FX, and such).

As Ken and Mett mentioned, try changing your 50 changes to something else.
If you have a plug in/VST-I or FX that is strobing, roaming or cycling quickly it will dirty your project without doing anything.
 
To change the Auto Save settings
1. Go to Edit > Preferences > File - Advanced to access Auto Save settings.
2. To enable Auto Save, set the number of minutes and/or the number of changes between saves.
3. To disable Auto Save, set both values to zero.
4. Click OK.

From now on, your projects are saved automatically according to the settings you entered.Using File Versioning
SONAR can be enabled to keep previously saved versions of your project in a temporary file. You can revert to any of these saved versions or use the default of the most recently saved version.
When file versioning is enabled, SONAR retains a list of previously saved project files in your project folder. The most recent version retains the original name of the project. Previously saved versions are saved with a time stamp following the original project name in order of most recently saved.

I'll try minutes only, see what happens and post back. 
rev

I can't explain why you're getting such frustrating Save occurrences, but I'm happy I disabled that feature.  It was always saving at the wrong moment.
Now, I just hit CTRL-S every few minutes or if I do something great.  I don't think I've ever lost work from an unsaved crash, and don't have auto-Save interrupting me.

Slugbaby
I can't explain why you're getting such frustrating Save occurrences, but I'm happy I disabled that feature.  It was always saving at the wrong moment.
Now, I just hit CTRL-S every few minutes or if I do something great.  I don't think I've ever lost work from an unsaved crash, and don't have auto-Save interrupting me.

Same here. I don't use auto save at all.
I did 10 years ago. but once I finally realized I had a stable set up, I never looked back.
I've been burned once or twice but never lost hours of work because I save every 10 minutes anyway.

It's more of a question than a complaint. I've been Cntrl/S-ing for 30 years but I get involved and forget how much time has passed. In times gone by, the Save happened in a flash because I didn't have many plugs, sometimes it would Save while I'm working and still not be disruptive but recently I've been working with more plugs and tracks and the Save itself is slow. I have to sit back in my chair and wait. I'd be interested in the code behind that feature.