Zipfile versions increasing in size on every save

It seems like fitnesse is including every previous version of a zipfile when saving a page. Even if nothing gets changed, the size nearly doubles every time.

Here is an example of a page, where I just hit Edit and then Save again, without changing any content:

4,0K -rw-r--r--  1 jenkins jenkins  951 2013-09-10 07:58 content.txt
3,7M -rw-r--r--  1 jenkins jenkins 3,7M 2013-09-10 07:49 martin stange-20130909093411.zip
3,7M -rw-r--r--  1 jenkins jenkins 3,6M 2013-09-10 07:49 martin stange-20130910074904.zip
7,3M -rw-r--r--  1 jenkins jenkins 7,2M 2013-09-10 07:58 martin stange-20130910074959.zip
 15M -rw-r--r--  1 jenkins jenkins  15M 2013-09-10 07:58 martin stange-20130910075815.zip
 29M -rw-r--r--  1 jenkins jenkins  29M 2013-09-10 07:58 martin stange-20130910075817.zip
 58M -rw-r--r--  1 jenkins jenkins  58M 2013-09-10 07:58 martin stange-20130910075821.zip
4,0K -rw-r--r--  1 jenkins jenkins  314 2013-09-10 07:58 properties.xml


The problem is, that the filesize rises very quickly and if it is about ~2G, the JVM gets an OutOfMemory Exception ( depends on Xmx etc. of course ). 

We are using the latest fitnesse build ( Build #378 ) but it also occured on earlier builds. 
There are no logs that give any indication on whats happening.