Today when working with a 120fps 1280x720 project (shot with Sony HDR-AS100V) I for the first time am facing a peculiar problem. When I work with clips on Timeline I am unable to move forward on timeline by using the right arrow key when Timeline is zoomed into "normal/default" view. The cursor on timeline simply refuses to move forward (to the right). Moving back on timeline works as usual/expected.

Only when I zoom out close to maximum levels allowed by Timeline the right arrow key begins to function again.

To be more precise, sometimes when pressing the right arrow key the cursor does move one or two frames to the right and then stops, but most often the cursor does not move at all.

I attempted to repeat the problem by opening/editing two other Vegas projects but it seems the problem only exists whilst working with 120fps/1280x720 projects.

What could be the cause?

Vegas Pro 12.0 (Build 770) 64-bit
Windows 8.1 64 Bit
RAM 32GB
Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz
Nvidia Geforce GTX 660 Ti 2GB