Kirk, I can confirm this behaviour also; even when the setting is unchecked. PM always applies the datetime!
Another strange thing I noticed with regards to the date is this:
For a bunch of NEF files, I removed the date created within Adobe Lightroom. When I later opened opened the IPTC info in PM, instead of being empty, the date suddenly showed the current date
What was worse, no mather how I tried to revert it back to capture time, the date stayed set to the current day... I was able to fix this by removing the <photoshop:DateCreated> and <photomechanic:TimeCreated> tags from the corresponding .xml file and resynchronizing the IPTC/XMP data.
Weird.