Bug stories!

This is a thread where we tell our stories of bugs that we fixed or couldn't fix.

I'll start:
I'm making an OpenGL program in sepples and I was trying to glGetString(GL_VERSION) so I can see if everything is working on Windows.

Every time I even made a function call? My program would crash. I couldn't for the love of my life find this god damn bug and started shouting and planning to plant pipebombs at Microsoft.^[1]

Turns out I made a global object which when instantiated would call that function from it's constructor. It seemed reasonably appropriate to place that function call there for the moment since I'd remove it later.

When you don't have an OpenGL context? Any OpenGL function calls you make result in undefined behavior; read: program crash.

Your turn.

_{[1] Not actually. Although I should make a 'pipebomb microsoft to hell' doom clone.}

An image analysis library written by another in-company team destructively modified its input for no reason, and nobody knew about it because the author had left for Gensokyo. It never showed up in testing because a new dataset was constructed for each test, but under certain conditions you couldn't analyze the same objects twice. The first call would succeed, the second would get its indices confused and read in garbage.

When I raised the issue to the library team, they replied with approximately ``Line 1192 has no actual impact on the algorithm, so we've removed it. Our tests still pass 100%.''. Bug: fixed, mysterious issues we'd been blaming on test data for months: gone.

What we learned was ``If the language doesn't allow you to declare parameters immutable, make damn sure they're not mutated''.