Speed restriction disappears when entering flight level for step climb

Interesting issue that I noticed today in the 737-700:

Before takeoff I entered a flight level for a step climb on the CRZ page. After takeoff I noticed that the 250/10000 wasn't followed by the AP and the CLB page showed a dotted line below SPD REST. Solved the issue with speed intervention. During the flight I performed the step climb, but I did not clear the field on the CRZ page. While doing the descent preparation, I noticed ---/----- below SPEED REST on the DES page. Entering 240/10000 and pressing Execute resulted in the same dotted line. However, clearing the STEP field on the CRZ page resulted in 240/10000 showing up on the DES page below SPEED REST. Just to be sure that I didn't make this up, I tried to replicate the issue and it did occur every time I entered a flight level for a step climb on the CRZ page.