As carriers increasingly turn to partner carriers to expand their networks, more and more travelers are running afoul of dreaded “no mileage fares.”

For travelers on legacy carriers, published fares are generally fine. And the only tickets that generally don’t accrue mileage are those booked on opaque sites like Priceline and some unpublished consolidator fares. However, with airline partners, many discount fares either give only fractional mileage or deny it altogether.

While airlines certainly have a right to do whatever they want, the maddening thing from both a traveler and travel agent perspective is the sheer randomness and inconsistency of the rules. Two regular clients of mine discovered this random reward factor with Austrian Air recently with published business class tickets for a flight to Vienna.

The tickets were booked on United and Lufthansa outbound, with Austrian Airlines and United on the return, using a discounted fare of about $3,700 roundtrip, booked in a P class. It was a joint fare. As far as corporate and travel agent contracts, the three carriers along with Swiss, are treated identically; although, from the West Coast, only United, Lufthansa and Swiss have direct flights to Europe.

I wasn’t concerned when the best connection for my clients from Vienna turned out to be a Austrian Airlines connection via Chicago to United. Later, when I saw the clients had received miles for their outbound flights but not been awarded miles for the Vienna to Chicago portion, I figured it was a mistake. So, I sent in the ticket copies. No, it wasn’t a mistake.

Austrian Airlines has, at least for now, decided to go their own way with discounted business class tickets — there is zero mileage accrual. Oddly, most discounted coach tickets are no problem. A $1,400 coach fare would have received full credit. (United did give them mileage for Chicago to San Francisco, at least.)

While the clients aren’t the type that completely work their schedules around miles, this flight was almost 5,000 miles and would have made the difference in them getting, or not getting, status for one of them for 2014.

Moreover, while this flight was booked as Austrian, it would not have made a difference at all had we booked it as a United code-share, as Mileage Plus says the “operating carrier’s” rules apply.

Fortunately, we learned this lesson in time so that she was able to make sure a December trip was on United and thus all ended up well with gaining elite status. But one has to wonder, how many other travelers, even experienced travelers, just assume that a business class ticket gets at least basic mileage credit?

In a perfect world, the system would be consistent. In an imperfect world, the lesson here is that if you really are counting on miles, especially with a partner carrier, double check carefully with any fare to insure that it allows for accrual. And, to be really safe, if it’s at all a gray area, keep the name and date of the person with whom you speak or a copy of the page saying that the fare is eligible.

This may prove to be unnecessary extra work. But, it could save a last-minute mileage run, or worse, falling just short of elite status.