Pneumatic Morso pulling moulding up out of clamps

[Gingernix]

Hi Folks,
I've got an old fashioned pneumatic morso which is great on narrow moulding but when I put anything broader than 3cm it pulls it out of the clamps- usually causing damage by hitting blade guard. Had to ask my neighbour to come and help hold down moulding while I tried to cut it.
Any suggestions as to what might be causing this?
Thanks folks

[grahamdown]

Have you tried cleaning the face of the blades? in my experience this only happens when either the blade face has residue on it or the blades are getting blunt.