1. Not working according to design (of programs). This is the mainstream sense.

2. Improperly designed, This sense carries a more or less disparaging implication that the designer should have known better, while sense 1 doesn't necessarily assign blame. Which of senses 1 or 2 is intended is conveyed by context and nonverbal cues.

3. Behaving strangely; especially (when used of people) exhibiting extreme depression.