I have been generating a simple square + dc signal in arb. mode. As seen both from an oscilloscope and a lock-in triggered by the SYNC signal, the resulting signal seems to move erratically between two phases (as a result, the lock-in is periodically unlocked). This does not happen for specific frequencies (like 2.0, 1.6, 1.0 ... MHz). Apparently, no matter the number of points in the arb. signal. Going back to the built-in functions, I do not encounter this problem. It is reproducible on another 33120.