Currently, if you select a beam in the Steel Beam Module, select a new size, click Analyze, and then click Update Database, that size is permanently attached to the member (i.e. frozen). However, if you select a beam, click Optimize, and then click Update Database, that size is NOT permanently attached (i.e. not frozen, or in other words it's optimizeable still). It doesn't work this way in the Steel Column Module (it always freezes the member when you click Update Database). I think it makes sense that beams should be frozen if Update Database is clicked, because it's a manual user assignment, regardless if it's an "optimal' size or not. If someone wants to keep beams optimizeable, then he/she can simply clear the size and click Design All.
This is purposeful. The idea being that if the user has decided to re-optimize the design, then that design should be set to be reoptimized eagain in the future. This returns the beam to the original state which is the most commonly desired condition. While you could use the Process - Clear commands to achieve the same thing, there could be some confusion around clearing the "size" and clearing the "design".
If you are reviewing a few beam designs and reoptimizing some, and you want to make sure the end results are all frozen (maybe because it's construction documents time), do that using Process - Freeze Design...
As for why Steel Column module is different, I think it's more common for column design to be user-frozen. Original trial groups lead to 3 designs that are all good and the user can pick. They usually don't want these designs changing unless it should fail later on, so Update Database here does freeze the entire column line. The re-optime tool in the steel column module view/update dialog barely gets used at all.