I'm not aware of any issues. I suppose one could build out a level 25 party, and run a combat with a level 25 encounter, but I'm too busy coming up with level 3 encounters for my current group
My impression with the way things scale is that the monsters' defenses go up one point per level. You're given a point every other level (BaB), and the onus is on the player to make sure the character makes up the other half level by some other means- periodic attribute increases, magic weaponry (+1/5 levels), powers, etc. As your tactics increase, you'll be using combat advantage more (flanking, attacks from stealth), and other tactics more effectively as your party learns to work as a team. The scaling is front-loaded with high starting attributes, and powers, gear and tactics take over later on as the bonus from attributes starts to become a smaller part of the overall bonus. There also seems to be a bit of a "shotgun" effect as characters advance, with characters getting more opportunities to make attack rolls, with a lower chance of each attack hitting.
The following is off the top of my head, with no reference to rulebooks:
By level 30, you're facing monsters with defenses 30 points higher than level 1 monsters. At level 30, you'll have a +15 from BaB, presumably packing a +6 weapon, will have an additional +2 or so from attributes (guessing here- could be more), which leaves you only a +7 to scrounge up. Given that a tricked-out level 1 character can be looking at about an 85 percent hit rate without CA, that means your equivalent level 30 character is still connecting about half the time, before considering tactics and situational powers. Seems to scale OK to me...