Odd Blocking Issue

I don't understand why a CREATE PROC from 3.5 hours ago is the head blocker. The SP wasn't changed since in months so this must be a compile/recompile? It's not a COMPILE lock though but a PAGE lock. It's certainly not the initial creation. What else can be done to debug this? It's happening and usually resolving itself in 4-6 hours or if I kill the head blocker myself. It doesn't happen every day but almost every day.

I've retrieved this info about the blocking from DMVStats and found similar info using my regular blocking info script also pulling info from DMV's.

I'm running SQL 2005 SP2 Enterprise.

statement started 6:35AM
waiting statement (PAGE lock):

insert into grades (blah,blah)
select blah blah from homework join blah blah

statement started at 3:01AM
blocking statement: =============================================
-- Author: <Author,,Name>
-- Create date: <Create Date,,>
-- Description: <Description,,>
-- =============================================
CREATE PROCEDURE [dbo].[ResultsHomeworkDelete]
@homeworkResultId int,
@NumDeleted int output
AS

delete homeworksessions where homeworkresult_id = @homeworkresultId

set @NumDeleted=@@ROWCOUNT

delete homeworkresults where homeworkresult_id=@homeworkresultId

set @NumDeleted=@NumDeleted + @@ROWCOUNT