If I throw the line far away from me the "floater" sinks a bit (which is normal). However, if thrown close enough to you (that is, when you right click the fishing rod), it sinks first and then flies up at this level (shown in picture).
It only happens if the line is thrown near you.
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-11877. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.