Weird transport behavior

I have been having difficulties with both Ardour 4 and 5.12. The transport (the line that moves when recording?) behaves erratically when recording and not during playback. It jumps forward and keeps moving at a high rate of speed. I have been using Ardour for a few years and Ardour 4 for a few months. This behavior appeared within the last week or so. What can I do?

It is hard to help you without a bit more information, answers to these questions may help track down what is causing the issue:

Is the issue you are experiencing the same with version 4 and 5.12?
Are you using an official build/release?
What platform are you using (Mac/Linux)?
What audio system are you using (JACK/ALSA/Coreaudio)?
Does this occur with all sessions?