Hough Circles in OpenCV3.0 vs OpenCV 2.3.1

Question

I have an input image with 4 circles and I want to use the HoughCircles function in OpenCV to identify the circles. I am using the OpenCV version of C ++ for Windows x64. Below is the pseudo code I used to detect the circle:

Read input image
Convert it from RGB to Gray scale
Gaussian blur
HoughCircles

I tried the above pseudo code in OpenCV 2.3.1 and OpenCV 3.0. Although I used the same parameters to blur Gaussian and HoughCircles, OpenCV version2.3.1 identified only 3 circles, while version 3.0 correctly identified 4 circles. I understand from the change log that version 3.0 has a new algorithm for HoughCircles, but I don’t know enough about the method to understand what has changed.

Is the behavior expected? Is HoughCircle detection in OpenCV2.3.1 lower than OpenCV3.0?