This issue is no longer reproducible in CA PPM 15.3
1. If 'Idea Type' is a pull-down, once you select a value from that drop down, the 'Idea Category' pull-down values are available to select. You can change 'Idea Type' back to '[--Select--]' if you do not want to have a value populated there and the 'Idea Category' will still work.
2. If 'Idea Category' is a browse display type, and 'Idea Type' is a pull-down, you can click the x in the 'Idea Type’ field and then the 'Idea Category' field works as expected.
3. Change the 'Display Type' of 'Idea Category' to 'Browse'.