Linux Xubuntu 13.10, x64, kernel 3.11.0-15-generic
AMD Radeon HD6850 1Gb
Broken: 2.69.11 77290fc
Short description of error
I am not sure if it's a bug or a feature, but tab mouse scrolling works only if tabs touching the left edge of screen. (Ctrl+mouse scroll is ok though)
Exact steps for others to reproduce the error
Split 3D View (or any other editor with tabs) vertically so you have two similar windows. Tab mouse scrolling works in left window which touch the screen edge, but doesn't in the right one.