There are cases where an RCS operation is aborted, which may leave a dangling semaphore file, whose name usually starts and ends with comma. If that happens, subsequent RCS operations for the same file fail until the semaphore file is removed.
There should be no practical value for a dangling semaphore file. So it's better to be removed before an RCS operation. As far as I observe, TWiki::Store::RcsWrap::_ci() and _lock() are affected. So both function will remove the semaphore file before executing an RCS command.