In SAP 9.2 PL04 and higher SAP have change the behavior for a field being set to enabled = False. Prior this was only for the mode the field was currently in but now enabled = False stay disabled despite mode change.
B1UP Module "Make Items Read Only" can't cope with this unannounced change currently and this result in if you make a field read only in OK mode it stay read only when you example with switch to find mode.
As a workaround you can manually enable the field again via a B1 Validation that when example switch to Find mode run an Enable($[$item.col.type]) command that open the field again.
SAP disabled this logic again in 9.2 PL07. The only solution is to upgrade to 9.2 PL07 if you are affected by this issue.