If it's shin splints, you could get it from horrible cycling mechanics. The tibialis anterior dorsiflexes (pulls up) your foot. If the muscle it under too much load while it contracts, an eccentric contraction results. These contractions are responsible for much of muscle soreness. If you are using toe straps, I could see it happening if your foot was not far enough into them, and you pulled up with your foot. Soreness could also result from locking your ankles in a dorsiflexed position, which could plausibly happen if your seat were too low.This would put a large torque across your ankle while you were contracting the tibialis anterior. The same thing happens to beginning runners who land hard on their heels.
Both of these possibilities would be obvious to an experienced
I don't mean to imply this is your problem, but I'm sure it has happened before.