Steps to reproduce:

1. open item with two preprocessing steps
2. remove first step
3. add another step
4. modify both steps to be invalid (i.e. missing pattern in regular expression)
5. press "update"

Result:
Validation error, as expected, and one preprocessing step.

Expected:
Correct old input (two preprocessing steps).

The same issue is observed in item "massupdate" view for "Preprocessing steps".