Ways for grinds to get into your cup:
1) If you tamped your group handle on a surface with spilled grinds & some of the grinds stuck to the spouts (because the spouts were probably wet from the last coffee or from a wash).
2) if the coffee filter (or "basket" if you do americanspeak) is cracked and grinds come through with the liquid. This happens with old filters that have suffered from a *lot of overpacking, and they eventually crack round the bottom "corner" where it is hard to see.
3) If you have overpacked the filter and when you insert into the group, grinds are pushed out onto the sealing rim at the top, the group seal doesnt seal, & coffee (brew) leaks out over the top of the filter / group handle during brewing, and runs down the outside of the group handle and into your cups.
4) same as 3) when the group seal is worn out / old / or buggered in some way!
I think that about does it.
OR maybe.....if as you say the new coffee filter that you bought is not a snug fit into the group handle, then again, you may have some leakage of grinds out of the top of the filter while you are brewing, and they find their way down into the cup as per 3) above.
One of the above I should think, because grinds absolutely cannot get through the minute holes in the filters as the grinds are much bigger than the holes.
very first CS site SponSir.