Linux Mint 2.6.38-8-generic 64-bit
geany 1.23 (git >= 550b2c1) (built on Dec 14 2012 with GTK 2.24.4, GLib 2.28.6)
I finally figure out how to reproduce this (I had emailed the issue on the devel mailing list).
The problem is that it doesn't wrap around when you press Ctrl + PgUp/PgDown to switch tabs on the side panel.
The cause seems to be related to hiding the documents list.
Steps to reproduce:
1. Go to "Preferences -> Interface -> Sidebar -> Show documents list" and uncheck the box, apply, and hit okay.
2. Focus the sidebar and press Ctrl+PgUp or Ctrl+PgDown multiple times and note that it gets stuck when it would have gotten to the Document List.