Alas! You found out one of the biggest problems concerning RM!
This engine is not suitable to do moving platform without a little scripting, you can just create a sort of "fake" platform effect this way:
(I haven't got RMVX, so I'll write it in a sort of text form)
Event 1:Platform
Trigger: Parallel Process
Page1: >Variable[1] = Game Player's X
>Variable[1] -= This Event's X
>Variable[2] = Game Player's Y
>Variable[2] -= This Event's Y
>Condition: if Variable[1] == 0
>Condition: if Variable[2] == 0
Move Process: this event
Move Process: player (same movement as event)
Wait for movement completion
Wait 20 frames
>end
>end
This is a sort of placebo effect, try and let me know

I hope this can help,
Jens