When Automatically Write Changes Into XMP is enabled, LR won't write the develop settings of the current photo when it exits. To reproduce:
1. Enable Automatically Write Changes Into XMP.
2. Edit a raw in Develop.
3. Change the Exposure slider to -5.
4. Exit LR.
5. Edit the raw's .xmp and observe that the Exposure slider is not -5.
See the attached screen recording. Prior to LR 11, this behaved correctly. With the current performance enhancements to writing .xmp, there's no performance reason why LR shouldn't write the .xmp of the current photo on exit.