I've never heard that WED had problems with concave blocks. 90% of all levels contain partially or mostly concave blocks, so I don't think that there can be a problem.

Still, you have to keep some things in mind:

- Concave blocks can't be used for building the BSP tree by the compiler. So when your level consists of only concave blocks, the BSP tree consists of only one huge leaf.

- When you manipulate blocks to make them concave, switch the map to "concave" in Map Properties to suppress the warning, and also lock their texture and set the block's "Concave" flag. This is not necessary for imported blocks because their concave flag is automatically detected and their texture automatically locked.

- Make sure that when using vertex manipulation on concave blocks, no surface is bent or broken. Otherwise, WED won't complain, but the blocks will look wrong.