OK, caught the bug on jp_n9's server, it only happens when ruby processes are started in suEXEC mode, user id is different from that of web server, and "max_idle_time" under "Rails" tab has been set.
When there is no request to ruby process for "max_idle_time", LSWS will try to kill this process group, but failed due to permission problem, but LSWS think the process group has been killed, when next request comes in, LSWS will start another group of ruby process, and so on.
I have updated ruby-lsapi-1.8 package to address this issue, please update your installation then and add an environment variable "LSAPI_PGRP_MAX_IDLE=xxx" under "Rails" tab to tell the ruby process to quit, the value should match "max idle time" value under rails tab.
We will fix this problem on LSWS side as well in 2.2.2, by finding a workaround for the permission problem of killing suEXEC processes, as well as setting "LSAPI_PGRP_MAX_IDLE" automatically.