Is it a hook and loop pad or sticky-back? I've converted a few of mine over to sticky-back and have that problem because I'm not using dust collection on them. I keep telling myself to buy or build a downdraft table, I think that would solve the problem, but I've been a bit lazy.
I've had the pads fall off several times. Right before they fail the thing gets very jumpy. You can either replace the pad, or do what I do the first time that happens, just drill three new holes and remount the pad. If you need to replace the pad, I've found that the Dewalt store has them for about 18 bucks, half of what the online price seems to be.
I really like the Porter Cable 33 series sanders. I have several that are over a year old and are used daily. Until recently a sander in my shop might be used six or seven hours a day for a week or more at a time. The only sander I prefer more is a Dynabrade.