Let's say that a thesis handles two different topics equally (e.g. 50% robotics & 50% mathematics). When the student completes the doctorate, can they apply for academic positions in both fields?

I have heard (from the mouth of an academic) that interdisciplinary topics can be a blessing or a course when it comes to academic employment. This is because the employers may think 'this person has not much expertise is robotics as half of his thesis is on mathematics - and they hire someone else with a clear non-interdisciplinary topic in robotics). Alternatively the employer may say 'this is the right candidate for us as he will give new dimensions to our departments with his/her interdisciplinary field...' and hire the candidate.

The same academic who discussed interdisciplinary PhDs with me said that many of her colleagues who did interdisciplinary PhDs are unemployed.

So, what do you think? Blessing or course?

*bump* Anyone got any input on this? I'm interested to see what people think too!