[Sunlite]

I did try to reproduce the issue and found the following.

OS: Windows 8 64bit
Calibre: portable 1.17

I can populate the 'find' field by either Ctrl + f or by Ctrl + c & Ctrl + v and the copied string contains the nbsp and the search is successful.

If I copy the string by right click and 'copy', the nbsp goes missing and is replaced by a normal space.

This is also visible by leaving the search out of the equation and pasting into the code itself. With the first way of copying, the nbsp will be marked as the others are. With the second method there is no mark.

Pasting into another application will show the same result. Existing nbsp with keyboard action, normal space with right click copying.

Using the 'copy' function in another application and pasting into ebook-edit does not lose the nbsp.