Wasn't happy with the B String from a set of Labella "Low Tension Flexible Flats"...
The intonation was all over the place...to get frets 1-5 to intonate, the rest of the string (higher notes) were out of tune...it sounded dead and was a general mess...just did not "ring" properly.
Put on a round wound B string I had around the house...it sounded terrible...
Got frustrated, and re-mounted the flat wound B string, and it sounded fine. No intonation problems, and it rang true...WTF?