Animating particle vector parameter in BP not working

[I’m moving this over from Rendering to see if I can get an answer from the BP sub-forum]

I think I’m missing something here.
I’ve exposed a Vector Parameter on my simple particle setup shown here (it shows Param Modes of Direct there, but I’ve tried Normal & Direct with the same result):


And connected that vector parameter to a timeline in the Blueprint shown here:

The parameter isn’t animated when I play. Is it that only certain parameters that work or is something goofy with 4.12.5?

I’ll try something similar in 4.13 to see if I can get that to work.

Let me know if any of you can think of a way to get this to work.