Wow, I've had just the opposite experience. Unless I slip the knot, my paracord knots are just shy of untieable. All paracord I've bought in recent years is the real-deal 550 stuff, but I do have some older cheap stuff from years ago before I knew the difference between imitation and 550. But I don't remember the cheap stuff having problems holding knots though.

Standard bowlines, though popular and well known, are not the most secure of loops. A finishing overhand in the running end is recommended for added security. Or use a double, water, or Eskimo bowline instead (if you want something in the bowline family).