Hello rhrtech,
The memory tests perform different types of tests which includes some of the following:
verification of data
ability to retain data
memory address value
bit switching
The difference in the short and extended tests is mainly the range of test coverage. The short test is designed to test a small range which included the area that reported the failure you were seeing. The extended test may have run tests in the same range, but may not have performed the same test on the same cell or location as the short test. What happens when you run the short test multiple times, does it always catch the failure at the same location?