There appears to be an issue with TurboTax calculating RMD for each distribution in isolation, rather than in aggregate as IRS rules allow. This post: https://ttlc.intuit.com/community/retirement/discussion/multiple-ira-rmd-and-actually-distrib[produc... says, "Our programmers are currently working to improve the RMD section experience. Be sure to sign up for email updates here: Why am I getting an RMD distribution amount error?"
