I recently had a business trip and used the train to travel. On the way back, there was a significant delay leading to missing a connecting train and as a result, I arrived more than one hour late. When being more than 60 minutes late, the train company will return you 25% of the train fare.
Due to this being a business trip, I will get reimbursed for the train ticket (which I had to buy myself). If I don't tell my company, they will never know that I got 25% of the return ticket back.
My question: Is it unethical not to tell them that there was a delay and I actually paid less than the original price? On the one hand, I would save them money. On the other hand, the trip was approved beforehand (with the original train price) and I was personally inconvenienced by the delay, not the company (as I was traveling back on a Saturday, a day on which I normally don't work).