Not sure if this is what you’re getting at, but it seems similar, anyway:
- Manually entered tasks with client selected from drop-down list = single row.
- “Current client” field returns a list of some kind (e.g.,
Filter(),Lookup(), etc). - Tasks created by button copy the list-of-one value to the client field, which looks identical to a single row value, but is actually a different object (list vs. row).
- Hence the two groups, because they are actually two different objects, even though they don’t appear that way to users.
SOLUTION: Convert “Current client” formula from returning a list to returning a single row by appending .First(), .Last(), etc.
What a coincidence that you would post this riddle today, @Paul_Danyliuk. I’m in the middle of a huge rebuild, and just caught this. It’s proving to be quite the pain to fix, and would have created nightmares if left undiscovered until farther down the road. I brought this issue up to someone at Coda long ago, but didn’t press the matter because I was too new to properly articulate why this hidden gotcha is going to be a big problem. I could probably articulate it a little bit better now… 
@Krunal_Sheth