I have an older (25yrs) PC690 and when I use straight shank bits, they tend to walk out... not fun. I don't have this problem with other bits. This happens with straight cutter bits or spiral bits, and it's happened with the 1/4" collet and 1/2" collet.
The router works fine, but not sure if it's me or I need to replace anything besides the collets.
For example today I was taking a 1/8 inch deep groove with a 1/4" diameter straight bit and it walked out to 3/8" after about 40 seconds (about 45" down the board. I was not pushing hard or in a rush. It came down over a 3-6" section, I noticed something was up and shut things down. I retightened it and did two more passes down to 3/8 without mishap... but this has happened several times now.
Any advice? I'm going to replace both collets (they are pretty old anyhow) and toss any bit that has slipped. (not a big investment, just 3 straight bits)