The Rotary Macerator is the more efficient version of the regular macerator, and it's behaviour used to take MV.
I'm using Tekkit 3.1.2, running on OpenJDK 1.7.0_04-b22 on FreeBSD 9.0 for a server; my client is Tekkit 3.1.2/1.2.5 on Win 7 with Java 7 (1.7.0_05-b05). I too noticed the Rotary Macerator didn't work (at least, as it had in the past) when connected to the output face of an MFE, but it didn't explode. Connecting to a batbox worked however, in my case.