The reason is that the amplitude & filter envelopes are in series. If one or the other closes, then there is your cut-off note. You were correct to increase the release time of the filter envelope to equal or more than the release time of the amplitude envelope.
Thanks to Rick Chadwick for the detailed troubleshooting procedure.
You\'re right Jake, if your filter is set up so that the envelope doesn\'t move the cutoff frequency, the filter envelope release setting will have no affect. None of the filter envelope\'s parameters will do anything.
The thing about Giga is that it has no simple amount knob with which to control the amount of envelope sent to the cutoff frequency. Most of the envelope control over the filter is strangely sourced from keyboard velocity. In order to have a setting which has absolutely no movement of the cutoff frequency you have to select specific velocity response parameters for the filter. I think they\'re a Non linear response curve coupled with Low dynamic range. With those settings, the envelope doesn\'t move the cutoff frequency, and the release won\'t have any affect.
If you don\'t need the actual filter, a simpler thing to do is just select \'none\' in the filter type box. This takes the filter and filter envelope out of the picture altogether.