I recall from years ago that tank-mixing with broadleaf weeds can result in reduced weed control. 

This is from the label:

"Tank mixes of CLETHODIM 2E and broadleaf herbicides may result in reduced grass control. If grass regrowth occurs, an additional application of CLETHODIM 2E may be necessary."

Further down:

TANK MIX APPLICATION OF CLETHODIM 2E AND BROADLEAF HERBICIDES
FOR CONTROL OF GRASSES AND BROADLEAF WEEDS
• Apply only to actively growing grass and broadleaf weeds at recommended height or growth stage listed on each label.
• Apply when the first grass or broadleaf weed species in a mixed population reaches the recommended height or growth stage for treatment.
• Apply under favorable soil moisture and humidity, which exist a few days after rainfall or within seven days after irrigation.
• Always add the appropriate adjuvant to the spray mix at the rate recommended for each specific tank mix combination.
• Tank mix applications may sometimes result in reduced grass control and possible increases in crop injury as compared to either product used alone. If regrowth occurs,
or an additional flush of new grass emerges, make a second application of CLETHODIM 2E as specified in the respective size and rate tables.
• Do not tank mix CLETHODIM 2E when broadleaf weeds are tall and/or dense enough to prevent proper grass coverage."

It has been noted here on AgTalk that always use Crop Oil with Clethodim.  However, on the label is specifies that when tank-mixing Clethodim with a fully-loaded Glyphosate, use NIS and AMS.  If tank-mixing Clethodim with a Glyphosate without adjuvants, then use Crop Oil. 

Check the label for this to verify accuracy.   ;)