using region I am getting PyramidTemplateMatcher: source is smaller than the target

Hi All,
I am using sikuli for the first time and it is excellent program to test GUI. During the development of the test suite though I run into the following problem:

Using region I am getting PyramidTemplateMatcher: source is smaller than the target

I have developed a script to test program's GUI. What I have found is that if there are more than one similar patterns on the screen sikuli matches them randomly. I needed to point to sikuli to match the one I need. Therefore I created a few regions where only one of the similar patterns is placed. Now I am the appropriate region to match the pattern and it works OK but I am getting the following message on the cmd line.

PyramidTemplateMatcher: source is smaller than the target.

I would like to know what is causing this message and why ?

My understanding is that sikuli is matching the pattern by looking in the region it is given, so it shouldn't matter that the pattern snapshot was taken using the default region (not the one is used for finding the pattern)

Many thanks in advance

Dimitre