Forbidden Combinations Showing Wrong Price


I have two sizes of product available in various pack sizes. I have created forbidden combinations so the customer can select the correctly priced pack size but if they swap between plant size then change pack size then go back to the original plant size it then shows the wrong price on screen but does actually show the right price in the cart but this will cause great confusion for customers, can any one help?

Please take a look, change the plant size then the pack size and then change the pack size back to see what i mean

CS-Cart version 3