In the meantime I found out the following 2 things:

1. If I call gsec with a local security database everything works as expected. The problem only occurs when it's a remote database. In both cases I used local gsec program.

2. If I don't redirect stdout to a file but say "gsec -display | more" I have the same problem: nothing is shown on the console (while it works with more and the local security database).

I hope this helps to solve this problem!