Inverting the input/output units in the unit conversion feature leads to "Malformed expression" error
Set the input unit combobox to miles, and the output variable to miles, then type some number. GNOME Calculator conveniently converts the unit live.
The problem occurs when you press the "Switch conversion units" button, symbolized by two arrows: ⇆ ...it inserts the unit names in the text field, which leads to this:
It should either parse natural language (which would be great) or not insert those words into the text box.