I've noticed some cisterns have siphon units that are not secured at the top. Every time the toilet is flushed, the top of the siphon moves or tilts to one side. For example, in the following youtube video.
https://www.youtube.com/watch?v=ijVUCgAWTF4
Is this part of normal operation, or is there is any merit to securing the siphon in these cases?