Map Window 5.6.4.26371 multi-field Labels

Hi guys, I have an issue where any label consisting of a multi-field expression is not saved or restored on map load. An example is for instance I have a Utility Pole shp file. Out of the available fields, if I use [PoleTag] from the attributes table (just one field), It works fine saving, exiting and restoring the map. If I use two or more fields in an expression like [PoleTag] + " " + [OBJECTID] it displays fine until I save the map and exit. Upon reload, there is no expression even if the points’ labels are visible. Save the map again, exit and re-open and now no labels are there at all because we lost the expression on the first save. The Shape file has only about 3900 point type shapes. Both fields are populated by a value. PoleTag is a string and ObjectID is a numerical required value. Both fields together are still less than ten characters.

Is this a known issue? Can you reproduce it? Thanks for any insight.