[Drewski_Brewski]

Originally Posted by chapteryx

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But I've run into a problem with non-breaking characters.
If the value that I enter into the custom property field value
(Prepare, Properties, Document Properties, Advanced Properties, Custom, Value) contains a non-breaking hyphen, then that non-breaking hyphen is transformed into another character that LOOKS like a hyphen, but is NOT a non-breaking hyphen.
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Any advice would be most welcome - I suspect that I've hit an unresolvable bug. ...snip...

Thanks in advance for any help (or even commiserations )!!

I was having the exact same issue (Word 2010). I think it is not so much a bug, but a limitation of the custom document property. The standard non-breaking hyphen is part of Word's (modern) Unicode character set, but the custom document property is limited to ASCII characters only.
So, I found that the ASCII character to use for a non-breaking hyphen is called the "soft hyphen".
There are a couple ways I've found to use this (be sure to read the 'NOTE:' text, below, to avoid confusion):

Method 1) You can insert this character into the body of the document, then put it on the clipboard for use in the document properties. In Word's "Symbol" dialog, "Symbols" tab, find the "from:" drop-down menu in the lower-right corner, and set it to ASCII (decimal) or ASCII (hex), then find the "soft-hyphen" character. [#173 (decimal) or 00AD (hex)]. insert it to the doc, close the dialog, highlight the resulting hyphen, [Ctrl]+[x] to cut it to the clipboard. Then, go into your document properties and edit as required by highlighting the dash, then [Ctrl]+[v] to replace it with the soft hyphen character.

Method 2) While editing a document property (advanced document properties dialog), press [Ctrl]+[-] (the dash/underscore key, NOT the "-" on the numeric keypad).

NOTE: the soft hyphen appears as zero-width, non visible character in the entry field, but you will see the dashes in the property value once you select "Modify" or press "enter" on the keyboard. "OK" the document properties dialog, then refresh the field(s). You should now have non-breaking dashes!

Another note: In the "Symbol" dialog, "Special Character" tab, there is something called the "optional hyphen" which also uses the [Ctrl]+[-] keyboard shortcut. This is not the same character as the ASCII soft hyphen. In other words, the keyboard shortcut returns a different character when editing document properties vs. editing the body of the document.

Hope this helps!
-DB