Implications of repeatedly paying my mortgage by cash at the bank

[Iris Tunlaw]

Every month I carry cash to my bank branch to pay down the balance of my mortgage, I've been doing it in the last 6 months, because I happened to have cash.

I know if I do the same thing to my checking account, it could be flagged to the IRS as "structuring" or "smurfing", but does that apply to mortgage too? The key difference is that in mortgage I'm forced to structure it, because that's what's due.

Additional info 1 in case it matters: it's actually on my primary residence.

Additional info 2 in case it matters: the balance each month is roughly $4500. I just live in an expensive area where a 1920s row house costs 1M. 

Thanks very much!!