Session Length in BBT Anomaly

Greetings,

I've noticed an anomaly regarding the session length indication, and am not sure if it's a bug or simply something I don't understand.

My song is 79 complete measures long, and is in 4/4 time. The first 20 measures have a tempo of 100 bpm, and the remaining 59 have a tempo of 120 bpm. So, the tempo change occurs at the start of measure 21.

In what follows, assume the playhead is at the very end of the song.

If the playhead position display, up in the toolbar, is set to frames, then I see an indication of 7320600 both in the playhead indicator and in the session length indicator in the status bar (near the bottom right of the screen). These match.

Now setting the playhead position to show in time, and I see 2:46.000 both in the playhead position display and in the session length indicator in the status bar. These, too, match.

But setting things to show in BBT, at the top I see 80.1.00 and in the status bar I see 69.0.640.

So the session length in BBT, shown in the status bar at the bottom, appears to be at odds with the true value. The numbers suspiciously suggest it was the tempo change which caused this.

Or am I stupidly missing some vital factor? Thanks for any explanation which can be offered.

Thomas