Late summer and early fall can make some investors nervous, and it can make for some interesting moves by short sellers. It turns out that they shied away from the two most shorted stocks traded on the Nasdaq between July 31 and August 15, but moved on other short seller favorites.

While most of the moves among the most shorted Nasdaq stocks were fairly mild, the world’s largest semiconductor maker saw a notable pop in the number of its shares short. But perhaps most unexpected was a penny stock leaping into the top six, a small health care company that’s looking for a reverse stock split.

Also note that just three Nasdaq stocks had more than 100 million shares short as of the middle of August.

Sirius XM

The more than 251.42 million Sirius XM Holdings Inc. (NASDAQ: SIRI) shares short after the first two weeks of this month was around 15 million less than on the previous settlement date, which was the greatest number of shares short since March. The latest reading represented 17.5% of the total float. As the average daily volume declined in the period, the days to cover dropped from near 11 to more than 13.

Warren Buffett reportedly has trimmed his stake in Sirius. The stock ended the short interest period more than 4% higher than where it began it, though it was down about 6% at one point in the interval. The Nasdaq slipped only fractionally by the settlement date. The shares closed on Wednesday at $5.58 apiece, after hitting a new 52-week high of $5.89 near the end of July. The 52-week low of $4.05 was seen last summer.

AMD

By mid-August, Advanced Micro Devices Inc. (NASDAQ: AMD) had more than 147.70 million shares short. That was a retreat of about 3% from the total on the previous settlement date, and it ended three consecutive periods of rising short interest. The most recent reading represented 16.8% of the company’s float. It would take more than two days to cover all short positions.

AMD is seen as an increasing threat to larger rival Intel. The August 15 share price was more than 4% lower than on the previous settlement date, though the shares had been down about 11% a couple of days earlier. The stock closed most recently at $12.50, which is more than 10% higher year to date. Shares have changed hands between $5.66 and $15.65 apiece in the past year.

Intel

More than 100.81 million Intel Corp. (NASDAQ: INTC) shares were sold short as of the latest settlement date. Short interest grew around 9% during the period, rising above 100 million for the third time this summer. It was also some 2.1% of the company’s float. The year-to-date peak was more than 102 million, reported back in June. As of the latest settlement date, it would take about four days to cover all short positions.

Brian Krzanich was one of the CEOs who quit the president’s American Manufacturing Council. Though the shares ended the short interest period less than 2% higher, they have pulled back more than that since then. The most recent close at $34.71 a share compares to a 52-week trading range of $33.23 and $38.45, and it is around 5% lower than six months ago.