The legs slipping under a load is actually a common problem. The tripod is not necessarily broken, on a premium brand like Manfrotto, it just may need an adjustment.
This example is using the MT190XPROB tripod. This is one of the newer tripod Manfrotto makes, but generally speaking the legs on the middle to higher end will mostly adjust this way. Some of the inexpensive Manfrotto tripods may not be as adjustable, because to make a price point competitive with cheaper brands, you may have to cut something, somewhere.
On the 055, 190, MT190 and others with removable leg lock clamps, this repair is this simple:
Unlock the leg lock, turn the lever adjust screw 1/4 turn to the right and test it under load. If it slips, do it again. There is almost never a reason to turn the adjust screw more than a quarter turn at a time. Over tightening that screw WILL break the leg lever and possible crack the leg clamp or bend the leg tube. Cracked leg locks must only be replaced, since glue (even super glue) will not stand up to the stress. Bend or dented leg tubes will not telescope or collapse correctly, or may jam inside each other.
Also while you are at it, check the legs for sand and grit, cleaning and blowing out the leg clamps and any clamping surfaces or shims that may be inside the leg clamp. While not all legs have the shims, these are the wear points for the leg lock and will always be on the carbon fiber type of tripods.
Worn shims will never tighten correctly, not matter how much you tighten the leg lever screw.
If you have problems, click here to return the parts to us for reassembly.
If you are having problems, or for a tune up or for repairs, send your name, address, daytime phone and email address along with your tripod to:
108 Garner Road
Spartanburg, SC 29303
Once we have it, we will evaluate it and contact you. Please send us your daytime phone so we can reach you during business hours.
Lastly, if we are repairing your Manfrotto Product; we are recycling all broken parts and scrap articles. Almost nothing goes into the trash if we can help it.