LTC2666: Voltage output glitches when outputting negative voltages

I am observing glitches when updating outputs on a LTC2666 DAC (12-bit, part number LTC2666CUH-12-PBF), specifically for negative output voltages. These glitches are small (~5mV, 1usec) but are specific to writing DAC values below 0V. Details and description of my system are below. My questions are:

1. 1. Is this behavior expected? I didn't see it documented in the datasheet, and haven't seen this from other DACs, so it comes as a bit of a surprise for me.
2. 2. Are there obvious steps I can take to ameliorate/eliminate these glitches?

Thanks in advance for your help!!!

Here's an example, in which I'm driving a +-10mV 1kHz sine wave:

Zoom:

Operating conditions:

• Using command code 0011 (Write Code to n, Update n) to update a single DAC channel
• Voltage rails are +-15V
• Softspan range is +-2.5V
• Using internal reference.
• have tested this on multiple channels with the same result. I have also tested this with channels with no load attached and verified this result remains (and isnt obviously a result of some weird load behavior)
• I'm updated the DAC at about 250ksps.

Here's a snippet of how my LTC2666 is configured:

I am not using DAC_TOGGLE or LDAC (they are tied low and high respectively by the microcontroller).

Apologies for the necessarily somewhat incomplete description of my system, and please let me know if there's more info I can provide here.