We discovered a bug in our product. Nothing special, happens all the time. But this one was interesting – not only because it was not reproducible at developers site, but also because it seemed unexplainable and it disappeared after two weeks.
The problem appeared in a menu which looks like electronic program guide on a TV : multiple rows of different data and time running from left to right. And current time is represented by a single line from top to bottom. At least it should be a single line – in the error situation the timeline was in different place in each data row. “How can that be?” – we were amazed. Drawing a straight line across the screen should be straightforward and simple.
We investigated by experimenting with different settings and input data – looking for patterns for reproducing the problem on developers site. But to no avail. There was something we were missing, obviously. Something that was different for us and the developer. And we only found if out when, two weeks later, we also could not reproduce the bug any more.
So what happened? 30 October 2011, happened, European Summer Time ended.
Turned out that do reproduce the problem, you would have to set timezone in the program settings so that the difference from the local real-time would be more 3 hours. Our product is profiled for Europe only, but due to how different countries set their time (who does and who does not), in the winter there is not possible to get that big difference. So the bug disappeared.
And as developer was based in Denmark, they could not get that difference also during the summer time. In the end we discovered a way for reproducing it with “fake real-time” and it seems to be solved.