TurboTax will not treat your solo 401(k) contribution as a workplace retirement plan until you actually enter the self-employed retirement contribution. Alternatively, when you go through the traditional IRA contribution section you can answer Yes when TurboTax asks if you are covered by a retirement plan at work.
Also check line 12 of TurboTax's IRA Deduction Worksheet to see the MAGI that TurboTax has calculated.
