I have found a bug wherein a frame rate change in the project properties does not undo correctly.
I am seeing this in Vegas Pro 12 build 770 and Vegas Pro 13 build 428.
Please verify this for me before I report it to check it's not specific to my set up, and let us know what build of Vegas you're using and what version of Windows.
1. Open a new project.
2. Set the project properties to the "HD 720-60p (1280x720, 59.940 fps)" template.
3. Zoom in and move up and down the timeline a bit with the left and right arrows on your keyboard to check that works.
4. Change the frame rate in the project properties to 29.970 (NTSC).
5. Edit > Undo
6. Zoom in significantly on the timeline with the mousewheel or other method.
7. Try moving the cursor backwards and forwards along the timeline.
When I do this, the cursor locks up or misbehaves.
And worse than that... I have the internal preference "Show Unquantized event start" and "Show Unquantized event end" set to TRUE. I am working on a 59.97p project. If I change the frame rate to 29.97p, some of the event ends are highlighted in red, which is expected because they don't line up with frame boundaries. However if I set it back to 59.97p (by using Undo) they remain red, and I also get the problem with cursor navigation as described above. The only way to fix it is to reopen the project without saving.
I also tried this by changing from 50fps to 25fps and got similar problems.