The steps to replicate this issue are as follows:

• Login to CA PPM and Go to Advanced reporting and create a new Adhoc View on any Domain. For example Project Management Domain.
• Create Pre Filters for a few attributes and lock them

• Ensure the Report is Table Type
• Add Task Name, Task Start Date, Task Finish date to the columns
• Add Groups Project Name and Project Manager
• Add more filters in the "New Ad Hoc View" page using the OOTB attributes until the number of filters is 27 and the prefix to the name of the filters crosses "Z" and becomes AA, BB etc. 
• Now use Custom Filter Expression to filter the results based on Project Name and click on Apply. Project name in the below screenshot has prefix E so the custom filter expression used is E.

<Please see attached file for image>

 
When "Apply" is clicked, the order of the prefix on the names of the filters changes and the results are also not filtered as per the specified filter.
For example in the above screenshot, E is the prefix for Project Name Filter and that has been specified as the filter criteria in the Custom Filter Expression.
But on clicking Apply, the prefix on the Project Name Filter changes from E to something else and the displayed Tasks are not for the Project Name selected in the filter E.

CA PPM 15.2