I dled the cap. The problem is that it is constantly trying to switch animation frames while both are playing at the same time. Construct doesn't blend animations at all.
A way to solve this is to have two sprites, one for legs, and one for the upper body. The legs will run on different animations as will the upper body. To have these connected, put the hotspot on the bottom of the upper body sprite and the top of the legs sprite. Then do:
[ul] [li]>Always (every tick)[/li]
[/ul] +Set "player chest" position to object "player legs".[/code:3ssu2w7l]
That should work.