Memory leak on Version 1.8 MacBook

Load existing world and do nothing. Allocated memory starts ~ 52% but shortly rises to 100% 1011MB. Mem on F3 screen starts around 20-30%, but within 4 minutes is at 99%. FPS starts at 120 but falls to 0-7 in only a few minutes. This is with no action at all; no movement of the mouse or view. This is repeatable for me. I did not see such an issue logged for a MacBook and Mac OS, so am logging this though other server issues do mention memory leaks. My Mac is a 2.8 GHz i7 with 16 GB 1600 MHz DDR3 and a solid state drive. Prior to 1.8, no issues were seen with this setup. My Mac is fully updated.