Initialization of Metric Modulation

Following up on previous comments in other posts about metric modulation and clarification of what notation to use for slowing or increasing tempo. So setting half = quarter slows the tempo and setting quarter = half speeds the tempo. I created a small score with four systems and market first and third with Allegro tempo at default 144BPM. I then marked second with modulation half note = quarter note and the fourth with quarter note = half note and then played the score. Both of the modified systems played back slowly which was okay for number 2 but not number four. Using the inspector for each, I noticed the tempo was set to "follow text" and the value of 120BPM appeared greyed out. I then unchecked the "follow text" and the BPM of system 2 changed to 72 BPM. I then changed back to "follow text" and the tempo remained at that value and stayed greyed out. When I did the same for system 4, the BPM jumped to 288. After this manipulation, the playback of system 4 was correct. So the question is why doesn't just entering the tempo marking create the proper playback without the steps I performed. I did not check to see if this was a temporary issue that would be corrected upon closing and reopening the file however.