To my endless frustration, this happens to me constantly, to the point that I've learned that the arrows are too buggy to rely on and that I need to avoid having too many documents open as much as possible. Until I read this post it never occurred to me that it was interpreting my clicks as a double-click, as opposed to just bugging out randomly. They can be spaced quite far apart in time and this still happens.
Might I suggest--nay, beg, desperately on my knees--that this feature be removed entirely? There is already a toolbar button that creates a new document with a single click, as well as an option in the File Menu requiring two clicks, as well as the CTRL+N keyboard shortcut. It doesn't make logical sense for the scroll arrows to create a new document rather than scrolling when clicked too quickly; those functions are unrelated, the buttons aren't even present unless you have enough documents open, and it destroys the intended functionality of those buttons.
I use Geany for hours every day for programming and basically any time I open a text file graphically. Many times I snarl in fury and hopelessness, battling with this issue, and every time I do an update I open it with trepidation and excitement, holding my breath in the hope that this is the day the bug finally goes away. Finally in desperation I came here to report it, thinking that somehow it must have gone unnoticed (perhaps only I routinely open dozens of files and use the GUI to move between them?)--and now I see that it's actually an unintended consequence of an attempted feature, which explains everything.
Oh great devs, I beg you from the bottom of my heart! I wail and I scream in desperation! I will sacrifice five strong bulls and ten spotted goats to your glory! Only please, please free me from this curse. My only wish is the ability to move between open documents at will without unwanted blank new documents jumping into existence and undoing all of the scrolling I'd already completed by dragging me back all the way to the end of the list to stare at them, grind my teeth in fury, and start the long process again. Please, please, please let the scroll buttons be peaceful and simple and honest and usable.