Comment 3 for bug 904720

Hello Aryrosa,

I have checked your issue, but I think you might have a misunderstand something.
This is not a bug but it's behavior of OpenERP .

Product form view we have two boolean field (check box), 'Can be sold' and 'Can be purchase'.

If we have checked "Can be sold" then product become sellable same as when we have checked "Can be purchase" then product will become purchasable.

Now comes up to your issue.
You have unchecked the "Can be sold" checkbox then and then only you have faced the problem and you can see the Sale Tax field as a "Read-only" because If product is not sellable then we don't need to add "Sale Tax".

If you have to apply Sale tax and purchase tax then product must be sellable and purchasable. So If you want to displayed this field untill and unless you have to true this fields values ,means for purchase tax your product should be purchasable and for sale tax your product should be sellable.

Hope this will help for your, and this is not a bug so I am closing this issue.

Correct me If I am wrong.

Thanks for understanding!