I concur totally with the "dont use cheap pedals" statement as I have also suffered this exact failure!

I use the Roland DP6 metal/plastic sustain pedal (the one with the rubber 'foot' that you can trap under your heel or [in my case] under on leg of the keyboard stand to stop it migrating). There have been posts about this in the past!

I would definately expect the "Fill Trigger" to be a momentary switch, and I would be very surprised if the "vocaliser on/off" function wasn't momentary as well.

The latching switches tend to be used on older "analog" gear (Roland space echo?) wheras most "digital" stuff uses momentary triggers for everything e.g. all Zoom effect units (its easier to detect a 0-1-0 transition than it is to keep checking for 0-1 and 1-0)

A point about momentary switches - which is probably only significant when used as a sustain pedal - is that the switch may operate in one of two modes: Normally Closed (i.e. the contact breaks when you depress the pedal) or Normally Open (i.e. the contact makes when you depress the pedal). "Normally Open" is probably the most popular. A lot of keyboards (PSR 630 for one) have a sustain pedal setting to cover either situation (although it wouldnt remember it one the power was turned off). However I had to re-solder my DP6 because I'm using it on an Ensoniq which expects "normally closed" operation. The DP6 has a double-pole microswitch and so can be reconfigured quite easily; other footswitches sometimes have a "mode" switch will allows the footswitch to work in either mode. For trigger operations this probably doesnt matter - the trigger will be the rising or falling edge of a 0=1 or 1-0 transition and you get both for either 1-0-1 or 0-1-0 operations.

Hope that makes sense!