Water ingress - a warning

This is a warning for all those whose van is fitted with high top side windows, which are long and narrow with rounded corners.
A while ago we were out in the van, the weather was very hot and muggy and a thunder storm with heavy rain came on. As it was night time and we were going to bed we left the two high side windows open to get some air in the van. In the morning I woke to find a damp mark in the lining stretching from one upper side window, across the cab headlining area and over towards the other side of the van. I immediately thought the worst, that we had a roof leak. You can imagine how I felt until I worked out the real cause.
What had actually happened was that the rain had run from the open window into the channel in the black plastic window surround. The channel then filled up and overflowed onto the side lining of the van and then wicked right across the cab headlining.
The rain that came in seemed to have come off from the top of the window at the hinged edge and I think the problem may be the rounded corner of the upper edge of the window. I think perhaps water runs along the top edge of the window and then drips off at the rounded corner straight into the black channel.
On this occasion the window had been fairly wide open but a similar thing happened, to a much lesser degree, when the window was about halfway open and the rain was much less.
So now if I need ventilation at night [besides the roof vents] I only just crack open the upper windows and if I hear rain in the night I close the windows.

I managed to remove the stain from the van with car type upholstery cleaner applied sparingly with a nail brush.

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Thanks for the warning Squip
Cheers
Stevo

We tend to leave these vented this time of year just so it has a little fresh air circulating around inside, by vented I mean locked on the first notch presume this is OK? just thinking if we had a heavy downpour whether we could suffer similar problems?

CC
I believe that the first notch should be ok. At that tiny opening the rain drips from the window will still stay outside and not run into the black surround.
I think that it is a bit of a design fault really.
When in the Hebrides we were in a very strong wind with rain and even with the windows locked shut the wind was forcing a little water in.
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Anybody else found that baby wipes are great for removing stains?

Even soy sause stains from the roof lining on my imported Bongo