This one bites a lot of people because the drop-down arrow appears, so the file looks validated when it isn't. Setting showErrorMessage=True (and errorStyle='stop') fixes typing, but it's worth knowing that pasting a value into the cell still bypasses data validation in Excel entirely, so anything downstream should re-check values when reading the file back. Another gotcha: an inline list in formula1 is capped at 255 characters, so longer option lists should point to a range on a (possibly hidden) sheet instead. A quick round-trip test that loads the saved file and asserts dv.showErrorMessage is True makes a nice regression check.