Because the distribution was made after April 15, 2018, the excess deferral is taxable in both the year of the excess deferral and the year of its distribution.  The code P Form 1099-R shows that it is taxable on your 2017 tax return (the year of the excess deferral) and the code 8 Form 1099-R with the entire excess and earnings shown as taxable is taxable on your 2018 tax return.  Because the corrective distribution was not made by the deadline, it's indeed subject to double taxation, unfortunately.

If your filed 2017 tax return did not already include the amount of excess deferrals in income, you must amend your 2017 to add this income.  You can do this by entering the code P 2018 Form 1099-R into 2017 TurboTax if the form shows the gross amount as taxable.

I've revised my answer to indicate that both Forms 1099-R are correct.  Please read it in the forum.

I filed an extension because they were so slow about issuing the check to refund the excess contribution.  Since the extension changes the due date of the return is there any way to keep this from being double taxed since it was received before the new October 15th due date?

Unfortunately, no.  For double taxation to be avoided, the corrective distribution had to be made by April 15.  A filing extension does not change that date since the April 15 correction deadline is *not* tied to the filing deadline for your tax return (although in some years the correction deadline and the regular filing deadline happen to coincide).