TE/TC Sand getting by Air filter on 2014 TC250.

When I serviced my air filter I noticed that a small amount of sand was getting in at the very bottom of the filter. No matter how much I greased it up, sand still sneaked by. When I put the 300 kit in I put that foam weather strip, 3/8" thick, all around the mating surfaced of the airbox and so far it has worked very well at keeping the sand out. Anyone else noticed this on there bike?

No I have not had this issue personally.

But the ZipTy Racing team guys did and Ty Davis worked with the team filter sponsor UNI filter to design a compatible filter with a 2 layer sealing surface. They found that the filter sealing edge would walk away from between cage lip and boot sealing surface and slip out (sounds like this is your issue).
This is (will be) marketed as a ZipTy Racing product by UNI. Photos have been shot for posting soon.
I'm sure if you call ZipTy they may be able to sell you one, before it hits the website store.

Others have reported this and it seems to be the plastic subframe bending, might be why they put an extra screw in it from '15 models on.
I fitted a washer over the center pin so it pushes the filter down a bit harder as suggested on some KTM forums and I never had a problem.
Used a 2mm thick plastic washer and drilled the center hole to size.

Good to know it wasn't something I was doing wrong.

The sand just gives you a big bore.