Today at 3:57pm, I tried to shortsell a 1,000 shares of XYZ at market. I was filled at 15.39. The other 500 was not filled. I asked the broker why because it was put in at market. They stated that there was no uptick between 3:57pm and 4pm. I thought that was strange because there were many trades at 15.40, 15.41 etc. As a matter of fact it closed at 15.40. So, I think that there must have been an uptick between 357 and 4pm. OR Am I misunderstanding the uptick rule?
Sounds like an issue with your broker, who are you using? You can clearly tell from time and sales which trades would pass the uptick test and be eligible for a short sale.
Are you looking at prices at the same marketplace that your broker uses? Some brokers use local exchanges (or make a market themselves) and may experience slightly different prices than say the New York Stock Exchange.