Latest version of Quicken Windows is no longer capitalizing payees and categories. The preference is selected under "data entry and quickfill".
R63.19 Windows
For whatever reason "updates" sometimes change your selected preferences. It doesn't seem like any existing preferences should be touched, but they are. A quirk.
This is a known issue that was caused by the latest release R63.19 -
According to the information in this thread, the issue has been identified and will be fixed soon.