I think you might be misunderstanding what is happening.  When the difficulty drops low, a lot of hashrate comes in to another pool which isn't altminer most of the time, and takes most of the blocks during the low difficulty.  This leaves altminer to find maybe 1 or 2 blocks during this time, and continue to find the blocks when the big hashrate disappears from the other pool which was taking all the blocks.

Sometimes the big hashrate comes on to altminer and it will find multiple blocks quickly in a row during the low difficulty, but recently the big hashrate has been on a different pool during these times, and again, this is why during this time altminer doesn't get as many blocks, but because it's still getting the most blocks when the difficulty isn't very low, it is still getting around ~50% of the blocks total.  Do you understand?