Basically what I want to do is log into my char "BenSales" on my cellphone. Since it's on the bottom, I have to scroll down to see and click it. But once I release my finger after scrolling, the sub-menu (the list where to choose the charater) just closes and it selects another char.

Samsung Galaxy S4
Android 5.0.1
Pre-installed browser

Any ideas on how to fix that?

Try in landscape

I have this problem too, what you gotta do takes multiple attempts, drag down and hold, quick release and instantly click the character u want. Takes a while to get used to. Sometimes drag and hold and while holding click char u want works too

Indeed the bolded part worked after three or four times.

From how I understand the phenomenon, the submenu instantly closes once any action took place in it, no matter which. Perhaps it could be an improvement to differ between scrolling in the menu and clicking on a character.

Happened to me until I turned phone sideways
Was easier to scroll down then

Yep, landscape works for me too.. samsung galaxy note 5