Hi, Richa Rd!
This can hardly be named the bug, as everything works as desired
Extensions are mounted as loop filesystems with mountpoint /tmp/tcloop and don't consume RAM. It consumes about 16 kB of RAM to mount one loop filesystem irrespective to its size. So You will save 16 kB of RAM if You will delete flwm_topside.tcz from Your onboot.lst.
You can check Your already mounted filesystems calling "mount" without any arguments.
Each WM extension when loaded writes its name into the "/etc/sysconfig/desktop". You can have several WMs loaded and during "startx" only one of them will be envoked. You can write to "/etc/sysconfig/desktop" manually too, the changes will take effect during the next X server start.