Problem when import particles to maya through houdini engine

[yaohaosquall]

Hi~

I've got a problem when I import particle(bgeo or alembic) into maya.I created a OTL which is as simple as containing only a file reader node(or an alembic node for reading almebic file).I used it to load a bgeo file which contained only a particle primitive in maya through houdini engine.It seemed ok ,I saw the particles,then I created a custom attribute to access the attribute that I created in houdini,and used that attribute to set up particle instance.Again I got a fine result when I first played the animation,but once I stopped playing,I lost all the connection between particle shape node and instance node as well as my custom attribute on particle shape node. How did that happen?Is it a bug or I've done something wrong?