I must respectfully disagree with a couple of the comments. If what Buck is describing is a "c" and not a "pigtail", then the knot did not come undone (practically impossible with a properly tied improved clinch). Instead, the material broke at the knot. This generally occurs for one (or both) of two reasons: 1) you have some substandard nylon (either in whole or in part); 2) when tightening the knot the material was not properly lubricated.
Newer materials (often "strengthened" by pre-stretching or surface treatments) are often "harder." This often means that they are more subject to heat damage when tying knots or physical damage. "Older" stretchy materials were more forgiving. My recommendation is to throw the spool away (not worth the agro if it's bad and you can't really check for flaws) and carry a small lubricating pad if your spit isn't "greasy" enough. Tests have repeatedly shown that lubricating with something like dish soap increases knot strength dramatically. cheers Paul http://www.galesendpress.com -- Paul Marriner Outdoor Writing & Photography. Owner: Gale's End Press. Member: OWAA & OWC. Author of: A Compendium of Canadian Fly Patterns (co-author), Stillwater Fly Fishing: Tools & Tactics, How to Choose & Use Fly-tying Thread, Modern Atlantic Salmon Flies, Miramichi River Journal, Ausable River Journal, and Atlantic Salmon.
