Retirement tax questions

Based on my first pass through TT, where I figured out I had an excessive Roth IRA contribution, I withdrew the amount reported as excess by TT from my Roth IRA (including earning on that amount).  So now I'm stuck in the "endless loop" discussed earlier in this thread.  It seems that the recommended way of dealing with this is to "estimate" your excess beyond what is reported by TT and withdraw that amount (plus earnings) thus preventing the "endless loop".

So I called by brokerage firm to chat about it. The retirement specialist had to consult with his peers and review the tax law.  His response to was was that his firm used to get that question "all the time".  But he said they haven't been questioned about this issue in years and it was their understanding that the tax law was modified to prevent the "endless loop" scenario.  He also conceded that 15b goes toward you MAGI.  

So I pulled out another $300 from my Roth and I'm hoping for the best.  Why doesn't TT instruct it's user to remove an additional amount then the initially report excess to prevent the "endless loop"?  Since most of us are using TT in lieu of a CPA, I mean, are we just supposed to know to do this?