Perhaps relevant to the 139C:
From the Fluke 87V manual:
For better accuracy when measuring the dc offset of an ac
voltage, measure the ac voltage first. Note the ac voltage
range, then manually select a dc voltage range equal to or
higher than the ac range. This procedure improves the
accuracy of the dc measurement by ensuring that the
input protection circuits are not activated.
KeySight has the same message, word for word, in their manuals.