Steps to reproduce:

1. enter the zabbix root dicecory
2. initialize the frontend test environment: ant init-frontend-myslq
3. run the frontend test: cd ui/test; phpunit --bootsrap=bootstrap.php selenium/testFormItemPreprocessing.php

Result:
when add too much preprocessing steps, the add button would not display the current screen, and then if the test case want to add more, it would run failed.
Expected:
the case run succefully.