OK, so I initiated a report of this bug to Microsoft - here's a transcript of the chat session:

Welcome to Answer Desk.

Kxxxx Sxxxx [09:36 PM] : Hello and welcome to the Microsoft Answer Desk! My name is Kxxxx Sxxxx . How may I help you today?

Bob [09:37 PM] : hi Kxxxx, I'm trying to report a bug to microsoft in word 2010 relating to mail-merge filters

Kxxxx Sxxxx [09:39 PM] : a bug?

Bob [09:39 PM] : Specifically, when a field is tested for "is blank" word inserts another statement with an "or" operand invalidating the constructed argument. This problem is reproduceable

Bob [09:40 PM] : Sorry, I didn't see your response! Yes, a bug.

Bob [09:40 PM] : If there's another place to initiate this report, i'm happy to do so, just let me know, OK?

Kxxxx Sxxxx [09:42 PM] : alright, thanks for reporting that.

Bob [09:43 PM] : Is that all there is to it? I'd love to get it fixed. Is there any follow-up to the customer on this sort of thing?

Kxxxx Sxxxx [09:44 PM] : No, we can find a tech who can remotely fix this, but there is a fee of $99.

Kxxxx Sxxxx [09:47 PM] : would you like me to find a tech who can help?

Bob [09:47 PM] : Kxxxx, as the problem is in all copies of the software that I own, and is a reproduceable bug wouldn't it need to be fixed in a kb for the product? Also, as a customer, the idea of paying Microsoft $99 to fix a problem that they have in a product that they sold is not acceptable to this customer... This is not a usability or end-user error. I have used Microsoft for OS crashes and such in the past, but that's a very different issue than a customer reporting a bug.

Bob [09:48 PM] : In any case, am I correct in understanding that there is no further communication intended from Microsoft to me on this bug report?

Kxxxx Sxxxx [09:49 PM] : correct

Bob [09:52 PM] : Can you tell me what happens to the report I gave to you about the problem? I'm just trying to understand the nature of this communication channel and its effectiveness.

Kxxxx Sxxxx [09:55 PM] : It will be forwarded to the support team, and they will be looking into the issue

Bob [09:57 PM] : Great - thanks for your time, and hopefully Microsoft will be able to come out with a fix for this - I would appreciate that, and probably there are others using the product that would as well.

Kxxxx Sxxxx [09:58 PM] : No problem.

Bob [09:58 PM] : OK, goodnight and Happy Holidays!

Kxxxx Sxxxx [09:58 PM] : happy holidays to you too