Earlier today I was looking at tickets from Welwyn garden city to Cambridge over the weekend. I knew that there are rail replacemnt buses planned and was fine with that. However, when I went to book my ticket ( super off peak day return ) I was greeted with a waring saying that my ticket would only be valid on my specified replacement buses ( see picutre ) and am confused because a return ticket usually allows travel on any train. Is this an issue with Trainline being confused or can I genuinely only travel on the replacement buses I specify when booking my ticket as it seems an odd restriction. Thanks