It's something which keeps on coming up very frequently since long long back
1) Many a times orbit gets activated, so u move ur mouse pointer, the file started orbiting. Sometimes CMD+F6 (fit to screen) or sometimes saving the file snaps it out of it, but that rare...only sure solution is closing n reopening
2) History marker goes missing, only way to work around is to right click n use 'roll history marker here', sure solution is closing and reopening the file.
Fusion
