A-cat sails have a polyethylene tube sewn into the luff, 5/16 inch (8 mm) in Bimare/Zuccoli sails: there are 30 cm lengths of line sewn inside at the bottom and top to keep tubing from collapsing. The luff track slot is thin, and using tubing that is too large will NOT work.
If the tubing gets a little crushed or bent, it is much more difficult to push the sail up. AND it may pull out under tension, as you described. If so, put a strap around the front of the mast, or a bungee or a line through the clew, and tie it snugly but not too tight. IUt will not pull out then.

This tubing is larger at 3/8 inch in Ullmans, Ashby etc to match the larger luff track in Hall, Composite, Fiberform masts etc. Same problem, same solution: Either check and replace the tubing if crushed ($20) with polyethylene or harder polypropylene with 1/16 inch wall thickness.
IMHO 8 mm or 10 mm tubing is too weak with 1 mm walls and will not be satisfactory. Dont outhaul too much anyway....= wrong.

Dave Carlson
USA 196