Ubercart

When one first selects an attribute's option, other options are filtered appropriately based on stock levels, as they should be. However if after the user selects their initial option choices, they decide to select a different option, all options are displayed (regardless of stock level) instead of being filtered as they should be.

For example:

Two attributes: Size and Color, where there are three options available for each attribute (Size: Large, Medium, and Small) & (Color: Red, Green, and Blue). There is no stock of Large Red, Medium Green, or Small Blue items. Selecting large as your size properly filters your options for color to green and blue. Suppose you select blue. If you then decide you really want green and try to change your selection, red will suddenly be in the list of available choices -- even though it is not available.