It's normal. The tiny tact switches under the cursor buttons gather dirt and eventually fail after years of use. My 2500 is about 5 years old now, it has the same problem.
You have 3 options:
1. clean the switch. Usually works for a limited time. My cursor down switch started acting up last summer, cleaned it up, worked just fine until last week. Going to clean it up again this weekend.
2. replace the switch. Shop around for the best price.
3. replace the whole PCB board:
http://www.mpcstuff.com/mpc-2500-right- ... pcb-b.html- if several switches are acting up AND the jog wheel AND rec gain/main volume pots have problems, you might as well consider this.