Hi,
Mine does the same thing occationally. To me, it doesn't seem to be connected with the parking break in any way, but rather with the gearbox being reluctant to engage drive if the cogs are loaded up from being parked on a gradient. In fact, it's more likely to happen if I forget to engage the parking brake all together when I park. Never happens on level ground. When Drive is engaged from Park, there will be a slight drop in revs and you can feel the transmission loading up. This doesn't happen in these instances, so it's definitely not engaging. If I drop it into reverse, it will engage and I can then move back to Drive and set off. I don't have to back up at all - simply drop into reverse, feel the gear engage, and then drop back to drive.
Mine has always been like this and it doesn't seem to get better or worse after three years. I take care not to rev the engine when it doesn't engage, since I don't think the clonk when it finally does drop into gear is very healthy.
My uncle had a Jag that did the same thing through 6 years of ownership. I don't think it's unusual or anything to worry about.
Cheers,
Henrik