Log4j problem. not able to create backup for multiple jvm

Not sure this is the right folder, but please help me.

This is my log4j configuration file.

log4j.logger.test=debug, app1

log4j.appender.consolestdout=org.apache.log4j.ConsoleAppender
log4j.appender.consolestdout.layout=org.apache.log4j.PatternLayout

# Pattern to output the caller's file name and line number.
log4j.appender.consolestdout.layout.ConversionPattern=%d{dd/MM/yy,HH:mm:ss} %5p [%t] - %m%n

# Configure the file appender :  app1
log4j.appender.app1=org.apache.log4j.RollingFileAppender
log4j.appender.app1.File=d:/test/logs/test.log
log4j.appender.app1.MaxFileSize=1MB
# Keep 4 backup file
log4j.appender.app1.MaxBackupIndex=4
log4j.appender.app1.layout=org.apache.log4j.PatternLayout
log4j.appender.app1.layout.ConversionPattern=%d{dd/MM/yy,HH:mm:ss} %5p [%t] - %m%n

The observation is :
If I only run one Java application that creates this log file, then everything is fine. It is able to create backup file like test.log1 and test.log2 after it reaches file size 1MB.

The problem is :
If I have multiple Java applications (multiple JVM) that use this log file (this file appender) then I found it is not able to create backup file. It always stays at test.log after it reaches 1MB file size. The previous content will be just cleared and then create a new same file.

It might make sense but is there a way to over come this? This is to say I want to make it no difference from 1 JVM or multiple JVM for the log file behavior.

Thank you very much.