UPDATE: A new post will come once I go through all the corrections I've received.
You might have heard the recent uproar about certain pre-washed vegetables that lost their kosher certification. Here is the story as I have heard it from a few (anonymous) sources. Note that I have not done any journalistic investigation and have only asked one or two people about it. Take this with a grain of salt.
At a convention of AKO (Association of Kashrus Organizations) in November, there was a discussion about the preparation of pre-washed vegetables (see here and here). In the course of the discussion, it became apparent that the Star-K was following an halakhic position that is unacceptable to some other organizations, including the OU. It seems that the dispute is as follows.
All agree that there is only an obligation to check for bugs if infestation is a mi'ut ha-matzui. This is generally assumed to be 10%.* In other words, if bugs are found in 10% or more of the vegetable under question, every single vegetable must in turn be checked to ensure that it is free of bugs. However, if bugs are found in less than 10%, then one can eat the vegetables relying on the vast majority of bug-free vegetables.
But how do you determine the ratio of infestation? The general position is to determine the overall statistical existence of bugs in the number of vegetablee, e.g. the number of heads of lettuce. The Star-K, following R. Aharon Kotler's personal ruling to R. Moshe Heinemann, does it differently. They look at each particular serving and determine whether there is a probability under 10% that any given serving will contain a bug. If there is, then even if it is of a vegetable that is generally infested at a rate of more than 10% they do not require further checking (this was all explained to my rabbi by a source in the Star-K).
Here is the example given in The OU Guide to Preparing Fruits and Vegetables, p. 16:
Three large heads of cabbage are set aside for coleslaw production in an area where cabbages have been statistically proven to contain on average 1 insect per head. Together, they will yield approximately 10 pounds of the salad providing 32 5-oz. servings.The OU Guide states that R. Hershel Schachter rules leniently, like R. Aharon Kotler and R. Moshe Heinemann above, but "the OU has adopted the more stringent stance." The OU Guide states that R. Shlomo Zalman Auerbach ruled strictly and I have confirmed that so do R. Yosef Shalom Elyashiv and R. Yisroel Belsky.
Taking the first approach, a serving of coleslaw would not be considered mi'ut ha-matzui. Fewer than 10% of the servings of coleslaw could possibly contain a whole insect (3/32 servings). Taking the second approach, we would consider cabbage a vegetable that requires bedikah.
Returning to the current controversy, the Star-K was certifying romain lettuce -- that generally has a high rate of bug infestation -- if the particular batch under question would yield an infestation rate in each serving below 10%. The other kashrus organizations would have required checking this lettuce (or washing it in such a way as to solve the bug problem).
All of the above is a normal disagreement on an halakhic matter. Then came public statements and the full-page advertisements in Jewish newspapers, in which the OU had no part, that the Star-K was certifying bug-infested lettuce. The Star-K-supervised vegetables were declared infested and non-kosher, despite the Star-K checking and re-checking to make sure that the vegetables they were certifying were indeed bug-free (their representative said he went to the factory and, after checking, left without finding a single bug). The Star-K eventually conceded to these objections and removed their certification from the product under question (link I, link II).
* It is interesting that R. Aaron Levine, in his new book Moral Issues of the Marketplace in Jewish Law p. 33, quotes R. Yosef Shalom Elyashiv as being lenient on this matter and assigning mi'ut ha-matzui to 15-20% rather than 10%. This ruling was given specifically to the OU in regard to checking for vegetables.