Prior to v.6 FileLocator Pro used to work in a Just In Time (JIT) search mode. JIT searching only searches enough of the file to decide whether or not it is a valid result and not necessarily the whole file. This means that very little result data is collected during the search but also that when FLPro needs to display or export the result data the file needs to be re-searched (from the last search position).
In v.6 a 'Display Hit Count' option was added in the Options tab. This has a larger effect on the search functionality that you might expect because it effectively switches JIT searching OFF. FLPro needs to perform a full search of the file so that it can correctly calculate the hit count and since it's already performing a full search it also collects ALL the result data on that initial search.
JIT searching can be useful for searching very large files where the full results aren't necessarily required but can also cause unexpected behaviour if the original file changes, or is deleted, between first finding the file and actually performing a full search. Therefore the default behaviour in v.6 was to have 'Display Hit Count' on and consequently JIT searching off.
To revert FLPro back to the old JIT searching behaviour switch 'Display Hit Count' OFF in the Options tab.
Edit (26 Sep 2012): As of version 6.2 (Build 1271) users should notice a substantially lower FLPro memory foot print due to improvements in memory management algorithms.