This bug is particularly manifest in cost settings but it seems to affect all settings with float values.
I have a french WinXP Pro and hence comma as default decimal separator. Here's what happens on my system:
Let's assume translational energy per bang is set to 0.1. When I click on "Custom simulation costs" and the costs panel appears, it's printed as "0,1" (note the comma). If I click on Okay without changing anything, the cost is changed to 0, which I can easily check by reopening the costs panel. If I want to leave the costs unchanged, I must manually replace each instance of a comma by a dot. Bizarrely, clicking on F1 Default yields dot-separated costs which are hence correctly applied when clicking Okay.
I guess the problem is a discrepancy between the output decimal separator, which is locale-dependent, and the input decimal separator, which is ".". Since DB is in english, the best solution would be to set both to ".".