Midi and virtual intruments


could somebody confirm and explain the following behavior?

I have my plugin compiled as instrument and then I noticed that Midi events, coming from the processblock, also seem to be bypassed to the plugin Midi output. I discovered that in Ableton 9 having my plugin inserted as instrument and another Midi track its input connected to the plugin its Midi output. My plugin provides Midi event filter that also works on the processblock Midi buffer and I set it up to filter out Note events. This work pretty well when the plugin is compiled as audio effect only while I still hear Note messages if the plugin is an instrument.

Does anybody have the same experiences?