ArcPy inconsistently accepts SQL queries for MakeFeatureLayer or SelectLayerByAttribute

I need to buffer a subset of features in a particular feature class. To do this, I am first creating a feature layer (using a SQL query to select only what I want), and then running Buffer. So my ArcPy script includes this little function to buffer my handful of feature classes:

def funcBuffer(inFeature, outFeature, bufDist, querySQL):
    arcpy.MakeFeatureLayer_management(inFeature, "tempLayer", querySQL)
    arcpy.Buffer_analysis("tempLayer", outFeature, bufDist, "FULL", "ROUND", "ALL", "")

This works perfectly on most of my feature classes. However, there is one that fails. The Python error is:
ERROR 000230: Failed selecting with "OH_UG" = 'UG'

The help page for that error suggests that the SQL query is invalid. However,

• the field OH_UG exists, and there are some features with the value “UG”
• it successfully validates in Query Builder
• I can use it to Select by Attribute with no problem (python snippet from within ArcMap: arcpy.SelectLayerByAttribute_management("TransmissionLines","NEW_SELECTION","OH_UG = 'UG'"))
• similarly structured queries work on other feature classes

I’ve tried different ways of passing the SQL query and all fail: '"OH_UH" = 'UG'', 'OH_UH = 'UG'', """ "OH_UG" = 'UG' """

I revised the script to do the selection after making the feature layer:

def funcBuffer(inFeature, outFeature, bufDist, querySQL):
    arcpy.MakeFeatureLayer_management(inFeature, "tempLayer")
    arcpy.SelectLayerByAttribute_management("tempLayer", "NEW_SELECTION", querySQL)
    arcpy.Buffer_analysis("tempLayer", outFeature, bufDist, "FULL", "ROUND", "ALL", "")

and now MakeFeatureLayer works, but SelectLayerByAttribute throws ERROR 000358: Invalid expression — still a complaint regarding invalid SQL.

I attempted to select using a different (numeric) field in the table, and am still getting the same 000358 error.

So I am not sure what’s going wrong — is it the SQL, is it the particular feature class, is it gremlins? How can I work around the problem in ArcPy?