Web Inspector ListBox ColumnWidths reverts after editing

In the Web page designer's Inspector, a ListBox's ColumnWidths value reverts to its previous content when you leave the ColumnWidths field. A typical sequence is to enter a width such as 75% while the ListBox has one column, add more columns, and then try to enter a width list such as 33%,33%,34%: as soon as the field loses focus, the value snaps back to 75%. The same loss can affect other Columns-section values (column count, frozen count, headers, alignments) committed around the same time.

Column widths entered while a ListBox has a single column continue to work; only changing them afterwards from the Inspector is affected.