are you using the normal size merchant window or the shrunken one? Not that it should make any difference but it'd help me narrow down any possible problems if the following doesn't solve the problem.
when adding the merchant window to your ui are you using the textures file included with this ui? unless you have modified the textures xml to work with your ui you should use the one included in this ui. The reason your ui isn't finding WDT_Border is because that's what I named the border texture that i added to the textures xml for easy usage otherwise each window would have to have a seperate WDT_something with details of what textures to use where so i made one that would encompass all and used it in most of the windows..... the same thing that the eq programers did with the default ui. using my textures xml will also add the chain to the scroll bars. you also need to make sure that you have the graphics included of course the majority of the windows use the drakah_chatwindow.tga as the border graphic as that's the one I took the border from. if you want to add the textures to your own textures xml file you'll need to add the wtd_border section of my textures xml to your xml and that should solve your problem.
As far as the wrap around for the hotbuttons. You know I've never even thought about it and it's never occured to me to even look at why it does that. Off the top of my head you could trying adding the line:
<AutoStretch>true</AutoStretch>
No idea if it'll actually work but it's worth a try. I'll try to tinker around with it and see what I can do although I know there's no command to turn wordwrap on and off on the buttons it does it automaticly. You might also want to modify the size of the decal for the buttons make it slightly larger. Not sure if it'll work but heck what could it hurt. In the meantime I'll see what I can conjure up for you. Keep in mind though I'm not a mage. :op