open a screen in monitoring section that has two graphs (default screen might do).
do a drag-zoom on the left hand one, but do not release mouse button. move to the other graph, release mouse button there and click once in the graph.

time period from-to in the upper right corner of the scrollbar changes to "NaN.NaN.NaN NaN:NaN - NaN.NaN.NaN NaN:NaN"

with some creative clicking it is possible to get both graphs to change to error images about 'period' not being an integer, but i haven't got the exact steps down here (feel free to try it - click from one graph to another, eventually it will fail).

but that's not the worst yet

click on one of the graphs outside the graph wall area :
strtotime() expects parameter 2 to be long, string given [include/func.inc.php:311]

go back to monitoring -> screens again :
strtotime() expects parameter 2 to be long, string given [include/func.inc.php:311]

check the profile table :

web.screens.stime | 524 | 0 | 0 | NaNNaNNaNNaNNaNNaN

change the period - error message still persists and the incorrect value in profies table is not updated.

a) this should not happen, of course;
b) we should check what we pass to pages - even if we pass a string, we should not get php error;
c) we should check what we ave in the db. that is obviously not a correct value for this param.