I've just noticed that the latest Calibre installed E-Book Tweak 64-bit. Looks great

I'll start to fiddle with it, as I'm rearranging some Gutenberg texts

I've started one in Sigil a few days ago, so I'll finish it there, but I'll start the next in E-Book Tweak and see how far I'll get.
There is one thing that seems to be incorrect (cosmetic problem): The window titles have &-signs in them, presumably to denote a hotkey. Examples:
&Files Browser
&Inspector
File &Preview
If it makes any difference, the operating system is Windows 7 x64 Professional.