now the tool pullout sounds possible... Before this op it running some adaptive clearing and I noticed the floor had steps in it, getting progressively deeper I thought it was all part of the same controller issue - but it's quite possible the heavy cut I was doing has dragged the 10mm endmill down within the collet. I seated the tool up against the top of the toolholder, so when I am in from work I can check by lossening it up and seeing if it can be pushed up, if it can then that is my issue.

Thanks for your help - any advice on stopping end mills walk out of collets is welcome :D