I realize AM tuning is kind of an afterthought nowadays, but has anybody else experienced this problem: if I try to select an AM station by direct frequency entry as described on page 37 of the manual, I can do it for 3-digit stations, e.g., 940, but if I try a 4-digit frequency like 1270, the display says "invalid frequency" before going back to the station already tuned. Stepping up or down with the "channel" buttons works OK. There's nothing in the manual to explain this.