I'm running an SDS-PAGE gel in running buffer and Mark 12 standards. the gels are bis-tris gels. every so often the happens to be one well which has a large mass of stained sample at the very top of teh well, where the loading well meets the actual sds-page gel. there is a little streaking down the well sides but other then that the results seem normal. I was wondering if this was a mechanical error on my part in loading the gel. The pippette tip cannot reach the actual gel to puncture it b/c it is too wide and stops after a certain point. Any ideas?