DS QUAD: FRQ over around 1 MHRZ locks unit

DSO QUAD 2.60 / 1.52 / 2.53

If I set my DSO QUAD to SCAN/NONE 1uS CHA (A) DC/AC and probe a 1 MHRZ Signal with FRQ being monitored the unit will lock up.

if I use the internal signal generator set to SQUARE 1 MHRZ, It does the same thing.

If I do not measure monitor FRQ, it will work… I would like to measure/monitor FRQ.