mcs.vst~ read /write bug

Hi, I've run into a pretty straightforward issue in 8.6.4 on a Mac and I suspect it is a bug: the read or write message into mcs.vst~ doesn't trigger the expected dialog to read or write a preset that you get with the regular vst~ object. Instead you get a complaint that you need to specify a file name. Upon trying to load or write to a pre-existing preset, I get no error but the preset does not load or save.