Following is the exception encountered when using "Replace in String" step in PDI kettle. There is no variable or group name defined as GKTIMESTAMP in the transformation and regex based replacement is turned off, yet it appears in the exception message. The environment is of Linux 64 bit machine with PDI 5.0.1 stable version

java.lang.IllegalArgumentException: No group with name {GKTIMESTAMP}
at java.util.regex.Matcher.appendReplacement(Matcher.java:849)
at java.util.regex.Matcher.replaceAll(Matcher.java:955)
at org.pentaho.di.trans.steps.replacestring.ReplaceString.replaceString(ReplaceString.java:79)
at org.pentaho.di.trans.steps.replacestring.ReplaceString.getOneRow(ReplaceString.java:124)
at org.pentaho.di.trans.steps.replacestring.ReplaceString.processRow(ReplaceString.java:202)
at org.pentaho.di.trans.step.RunThread.run(RunThread.java:60)
at java.lang.Thread.run(Thread.java:745)

Can anyone suggest what could be the reason for such an error and how to resolve this error ?