use of subjunctive in interrogatives after verbs like penser

I knew that in inverted questions you use the subjunctive after verbs like 'Pensez-vous...'  If you start the question however with 'Est-ce que vous pensez...?' does that rule about the subjunctive not apply?  I ask because I had put 'Est-ce que vous pensez que ce soit un problème structurel' and this was marked with a correction to '.......c'est' instead of 'ce soit'