Tampons at Night...causing leaking?

I am still getting used to juggling my cup (it's only been my third cycle with it), so I tried using tampons during the night during the last two cycles.  Just because it's easier than cleaning it and such in the middle of the night.  But the next morning, when I put my cup back in, I cannot get it to stop leaking!  I put it in TWICE and it leaked twice, despite being fine for my first day (before I used the tampon).  I put it in the same way, sealed it the same way...is there a possibility the tampon is causing my cup to malfunction?  My period is very heavy, but it was basically the same between the first and second days...I don't understand it!

Any ideas?

Thanks!