Excel 365: Unexpected Predictive Behaviour Causing Retroactive Cell Changes in Structured Dataset

Hi everyone,

I’m posting this to share an unusual and potentially important issue I encountered in Excel 365 this morning. I’ve already submitted a detailed report to Microsoft via the Feedback Hub, but I felt it would be useful to document it here for visibility and to see whether anyone else has experienced something similar.

While entering data into a structured table (a parts‑catalogue workbook), Excel began exhibiting behaviour that did not match Flash Fill, AutoFill, or the standard predictive typing feature. Specifically:

Grey predictive text appeared beyond the cursor and extended into cells below the active cell

Excel began rewriting previously validated cells in the same column

Each time I pressed Enter, Excel updated earlier rows based on its latest inferred pattern

Attempts to correct earlier rows caused further cascading changes

Undo did not revert all changes

The behaviour resembled an AI‑style inference engine trying to “learn” my pattern, becoming progressively more confused

This was not the normal predictive typing behaviour (which only shows grey text inside the active cell and does not affect other cells). The behaviour stopped only after I clicked the Flash Fill button twice, which suggests an internal state reset.

I’m not seeing the issue now, and other workbooks behaved normally, so this appears to have been a transient internal mode rather than a persistent setting.

I’m sharing this here because:

it caused silent data corruption in a structured dataset

it may indicate an experimental feature or feature‑flag activation

others working with structured data may want to be aware

I’d be interested to know if anyone else has seen similar behaviour

If helpful, I can provide the reproduction steps, screenshots, and the engineering‑style report I submitted to Microsoft.

Thanks,

John