Good Paraffin for TMA's

I have run into a problem with something to do with the embedding process. I have bubbles in the blocks after they come off the embedding center. I'm not sure if it's air in the line of the new embedding center (Sukura) or with the paraffin (Shandon). Has anyone experienced any problems with the new embedding center? Could that be what is making these bubbles? Is it the paraffin, (I don't think so), has anyone seen these bubbles form in paraffin as the block cool or even the next day? Lastly any suggestions if I have to change paraffins as to which to try, needs to be hard to core yet we have to be able to produce good sections at 4 microns for H&E's. I don't process the tissue on site, so It's hard to trouble shoot but I have never seen these bubbles and I have been around for a long time.