Hi, your thoughts led me to some more experimenting.

Using your idea to capitalize whatever I'm inputting into the 'Client' content control to begin with, I have further narrowed it down to this: If All Caps is active, and the Display Names for your drop down are already all capitalized, it will work. If any letters of individual Display Names are not capitalized, those specific selections will not work, but selections that have all capitalized display names will.

It appears that the capitalization of Values does not break this, even if All Caps is on, and you input value's have lower case letters, it will still work.