If the new leaves are also really tightly packed together, I would suggest you are giving them too much light intensity. I had this problem once. I backed the lights off about 5 inches and problem solved. 10 inches doesn't sound too close, but lacking any other symptoms, that's my diagnosis.

Most growers say standards 10-12 inches from the bulbs and 6-8 inches for semis and minis.

I would start with putting these a few inches lower and see if the problem resolves itself.

Also new light bulbs, especially two new light bulbs would be giving you very intense light which will change in a few months. In the meantime, you can adjust the distance or you can put a piece of tissue in the center for a few weeks then see if leaves start taking a bit more room.

Nancy