Question about iTunes web pages and auto opening of iTunes

[BigBrother]

Hey all- apologies if this is covered somewhere, I've tried searching with no luck.

I've found that the behavior of iTunes app homepages can be really erratic with respect to auto opening iTunes. I'm trying to set it up so that when users go to my site, clicking on the 'purchase now' button takes them to the iTunes page and does indeed auto open iTunes. Not exactly rocket science here- just about what everyone does.

But I've noticed that, seemingly without pattern, sometimes the iTunes webpage will auto load and prompt me, sometimes not. Using fieldrunners as an example:

Fieldrunners

Try the bottom link to buy on iPhone. If you click it, it won't always try to open iTunes once redirected to Apple's site. It seems not only browser dependent (IE seem to permit it more frequently, little surprise), it's also inconsistent within each browser- I can't peg down if it's cache related, history, nothing seems to add up. Everytime I think I have it nailed, it'll either suddenly work or not, ruining my theory.

Thoughts?

Thanks!