Normally when you hover your pointer over an item it will turn yellow if you can pick it up. If you can not pick it up, aka its locked down or non movable. The item in this case will not turn a color.

The problem with some items. A good bit of them. When they are set to movable := 0 they still look like they can be picked up. You can not actually pick them up or anything. The effect is annoying just the same. Also, doors just as they are opening or closing, if you hold your mouse on them, they do the same thing.

This is more-so based on the tiledata in the client.

Any magical packet hook that can help?

No, its not server controlled at all. You may be able to edit the client files, however.