In IDEA the usual [alt] on my MacBook does not result in the '#' character. As can be seen from this post, it works normally.
I don't know if this is an issue with this release, which I installed earlier today, or if it is a configuration problem. I can't say if I had a problem before today.
IntelliJ IDEA 2016.2.3
Build #IU-162.1812.17, built on August 30, 2016
JRE: 1.8.0_112-release-b287 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o