There were some nasty memory leaks in VFP 6.0

Microsoft Knowledge Base articles reference some information on those.

818175 is "List of Memory Exception Bugs Fixed in Visual FoxPro 8.0"

818178 is "List of Memory Leak and Corruption Bugs Fixed in Microsoft Visual FoxPro 8.0"

818179 is "Miscellaneous Problems Fixed by Visual FoxPro 8.0"