The instructions for Form 990-T indicate that the deadline for the retirement account to file the form or request a filing extension is April 15. The extension is an extension to file, not an extension to pay the tax, so while the extension avoids a late-filing penalty if the form is filed by October 15, it does not avoid the late-payment penalty and interest which accrues after April 15. If the partnership is filing under an extension and does not issue the Schedule K-1 until after April 15, I'm not sure that it's possible to avoid a late-payment penalty and interest. It might be that the only way to avoid the situation is to not invest in investments that can generate UBTI.
