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This is actually a two part operation. You have already covered one of the parts. That is to ensure the "Auto-Synchronize" option has been enabled in the Window properties for the CHM.
The part you are likely missing is the "Always Show Selection" and that is enabled in the TOC properties. To enable this, edit the Single Source Layout properties. Then click the Edit button on the properties dialog. Next, click the TOC Styles tab. Enable the option labeled "Always Show Selection", re-compile and you should be set!