Q: Our handyman installed 23 1/4 X 45 7/8 vinyl casement windows in our home last year...

They have been working beautifully and are air tight when locked. This spring we noticed about a 2' long diagonal crack in one of the windows. Our handyman removed the window, brought it back to [the manufacturer] and was told that because we must have left it open under windy conditions it bowed the frame causing the glass to crack.

He said they demonstrated it to him.
Because of this, they wouldn't replace the window without our paying a replacement cost of over [price redacted]. just for the window itself. (Of course we paid more for the total replacement because of the labor involved).

Is this a particular problem with casement windows that by leaving it open when windy outside, the glass is susceptible to cracking? Or, are there better casement windows with a more solid frame that prevents this from occurring? We don't remember a specific time we left it open in a wind storm and it seems bizarre that we cannot now leave the window open when leaving the house or going to sleep because a gust of wind might crack the glass.
[Reader Name - Anonymous]

A: Therein lies one of the ironies of casement windows: they work great when sealed shut, but can be damaged when open...

Almost as bad as the cracked glass is the problem of the casement sash being torn off its hinges. Surprisingly, it really doesn't take much of a gust to do this, either.
As much as I deplore most of the replacement window industry, the people who spoke to your handyman do have a bit of a point.

Window sashes are strongest when they have the added strength of a surrounding window frame. Remove the sashes from the frames (in the case casements) and you place the sashes at a higher risk for damage.
One issue specific to you would be torsion. I have not done much research into whether casement sashes are manufactured differently than other sashes (double-hung, sliders, etc.), but I believe that torsional movement with an open casement sash would produce the type of crack as you describe. An open casement has 50% less structural stability than an open double-hung window because only one edge is stable.
As you mention, you cannot recall a time that you left the casements open during a high wind. Having the casements open during these conditions is the only way I can imagine that torsion would affect the sashes. All said, I'm not sure that you would have much of a case if you brought this up directly with the manufacturer or window company.

In contrast, one problem that most certainly is a failure of the window is when the seal fails, and the vacuum is broken and the inner argon/krypton gas escapes. Window manufacturers are well aware that this is a problem, but they do everything in their power to make certain that they are not responsible for any cracked glass.