Contact the author/Bug reports/Suggestion box
You can contact the author at dory36 at firecalc dot com.
For "why does it..." or "how do I..." questions, please visit the FIRECalc support section of the Early Retirement forum. There are lots of folks there who can help.
Before you report something you aren't sure is a bug:
Many questions have to do with whether an intended change is happening as expected. You can check this for yourself quite easily. start with a nearly blank scenario with zero expenses, zero inflation, and zero growth. Make a single change at a time and see the effect on the timeline. Make the change quite large, so the change in the graphs will be obvious. Remove that change and make another. Keep doing this until you satisfy yourself that your changes are happening as you expect.
Many other questions ask about specifics in the data, such as "what starting year failed..." etc. You can see the year-by-year balances for all the results and the formulas used for each cycle by checking the "provide data and formulas" option in the "Investigate" tab, as shown.