dear evernat,

thanks for your reaction. =)

our tomcat is running in version 7.0.52:

Server version: Apache Tomcat/7.0.52 (Ubuntu)
Server built: Jun 19 2015 08:54:46
Server number: 7.0.52.0
OS Name: Linux
OS Version: 3.13.0-63-generic
Architecture: amd64
JVM Version: 1.7.0_80-b15
JVM Vendor: Oracle Corporation

so do you think it would help to upgrade to version > 7.0.54?