When the Display Details Read-Only check box is selected, there is no need of acquiring the lock on WO. But Pega is still acquiring the lock. There is a condition in ProcessAction activity to skip pyAcquireObject activity call when param.EditConfig=="ROexpandPane". But that param is not getting set even though Read-Only checkbox is selected. Seems it's a product level defect.
The major problem with this issue is even when user collapses after the expand, the lock is not getting released. This causing serious problem. If user expands the row once in the grid, no other user can work on the item. Other users has to wait for the lock to become soft lock, because there is no way for the current user to release the lock if he don't want to work on that item.