I get the following error when expanding a hierarchical grid, using v9.1.20091.2055.  I wasn't getting the error using 8.3.  If I turn on and off the filter row using javascript, then expanding/contracting works fine.

 Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; WOW64; Trident/4.0; SLCC1; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.5.21022; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Zune 3.0)
Timestamp: Mon, 20 Jul 2009 17:12:32 UTC

Message: 'FilterRow' is null or not an object
Line: 6511
Char: 2
Code: 0
URI: http://localhost/test/WebResource.axd?d=JjUdJPQjKs1_UG9D0LTJ-UF8qlKOYZQaxUIiChFkuisPbULKfxT5VbWKmAaa6Y8rtzlh6XW0keCJZ9tASZixG2aevzf9ZyhZzPeO5mNpXJs_03gqiG_gaeHUtyvapmrZvga3NTBW2Ia8q4eaZm4e1TY4UmXp6TEwo-iQPE496zU1&t=633818869136432519