Observe your surroundings and talk about your experiences.
After nearly two months of being kept on the hooks about incurring additional cost when bus terminate halfway in order to keep up with the scheduled headway frequency, I finally found the solution to it.
Aside from my friend E telling me about getting a valid free ticket to take the next ride last Nov, I actually observed one guy doing on earlier on Monday. As such, I actively climbed back onto the bus and asked the driver for a similar ticket. After asking my boarding point, he pointed me to the guy in front and told me to follow him. Hence, I bore no additional cost for taking the next ride.
This morning, the same thing happened again. Before alighting, I went to the driver to ask for a free ticket/pass for the next ride. Without further questioning, he pressed a button and out came the ticket for my next ride.
Hope this little sharing will help the rest of you out there to save some transport costs in London!