Mueller, for those unfamiliar with his work, may be the world’s most-quoted expert on smartphone patents. In the four years since Steve Jobs launched his “thermonuclear” war on Google’s (GOOG) Android, I’ve quoted him in 80 different stories. In the main, he’s been supportive of Apple’s intellectual property claims and critical of countersuits based on so-called standards essentials patents, like the ones Samsung asserted in the first Apple v. Samsung trial.

But something changed between the 2012 trial — the one that resulted in a jury awarding Apple damages of roughly $1 billion — and the trial that began this week.

It started with a March 11 post that opened with an acknowledgment that in the past Mueller has “sometimes, maybe even quite often, but not always agreed with Apple,” but quickly shifted gears:

 “I face the first situation,” he wrote, “in which I don’t merely disagree with Apple but am rather wondering whether it has lost its mind.”

The issue that set him off was Apple’s demand, revealed in a January pretrial hearing, that Samsung pay $40 per patent for the five patents at issue in Apple v. Samsung II.

“$40 per unit,” he wrote. “For five software patents. Give me a break. Reality distortion would be a total understatement for this.”

If that weren’t enough to raise the blood pressure of Apple partisans, it was followed four days later with a positive recommendation for Yukari Kane’s
Haunted Empire
— a book that nearly every other reviewer panned.

Then, on Wednesday, Mueller issued two more rapid-fire posts:

• 10 European judges found Apple had not invented slide-to-unlock (star patent at Samsung trial)
• In 49 months of holy war, Apple has not proved that it owns any feature other than rubber-banding

It was those last posts that got the folks at AAPL Sanity talking about payola.

I asked Mueller about this charge in a March 18 e-mail: “I’ve noticed a change in the tone of your last two pieces, and I’m not the only one. Is there something I should know — or you should disclose — about your client list?”

His reply:

“If there was a change relevant to my blog, I’d disclose it immediately. The only change to my client list is the addition of a German automobile manufacturer. Car manufacturers increasingly have to address smartphone patent issues. This is unrelated to my blogging subjects.

“I am, however, increasingly skeptical of Apple’s chances. I expressed such skepticism on a few earlier occasions, such as after the HTC settlement.”

I followed up Thursday, after the two most recent posts. “If something is going to come out eventually,” I wrote, “I hope you would do me the courtesy of giving me first crack at the story.”

This time he mentioned that he’s developing an app:

“There’s nothing that could come out so I won’t be able to give you a scoop. But everyone can verify easily that I expressed the very same position on Apple’s pricing vs. Android before. For some time I thought IP enforcement could help Apple, but there comes a point when the results don’t suggest Apple will get serious leverage.

“The closest thing to a conflict of interests is something I’m transparent about in my recent posts: I will launch my app on Android first. (Second platform will be decided after launch, but most likely be Windows 8.1 because of desktop market share.) I consider this something relevant to disclose, but it’s not a conflict of interest per se because I wouldn’t have made that platform choice if not for the views I express. It’s like eating one’s one dog food, sort of.”

I have some sympathy for Mueller. When he was writing positively about Apple he was regularly excoriated by Google partisans who claimed that his coverage was colored by the fact that he has done paid consulting work for Microsoft (MSFT) and Oracle (ORCL), two firms that have locked horns with Google in the past.

Now he’s getting it from an even more rabid fan base. You can hear his frustration in his latest post — Apple does not ‘own’ multitouch smartphones and tablets any more than Samsung ‘owns’ phablets — in which he addresses the charges of payola directly.

“There’s a sense of entitlement in the Apple camp and it is centered around the notion that Apple, because it reinvented the smartphone (I agree) and built the first popular tablet in history (I agree, too), has exclusionary rights that give it serious leverage over Google and its hardware partners (on this one I disagree for non-philosophical reasons after watching Apple’s lawsuits for several years)…

“I did some work for Microsoft and announced it a long time ago; that does not make me a “mouth piece”. I also announced a working relationship with Oracle a long time ago; same thing — and when the appellate decision in Oracle v. Google comes down, a lot of people will suddenly see that I was right. As for Apple, I addressed that one further above, and if I had had in an alternative universe an opportunity to work for Apple at this stage, I would have been unable to comment on this trial publicly because of my fundamental disagreement with Apple’s damages claims and its disproportionate infringement allegations. My opinions are not for sale.”

There you have it. He’s on the record now.