8722D Error 61 - restoring learn string and cal arrays

I'm using an 8722D and need to  store learn strings and the cal arrays to disk, then restore them when needed. After restoring the learn string, I have an intermittent error 61 SOURCE PARAMETERS CHANGED when I send CALIS221 (for example) to beginning sending the cal arrays.  Then when I send the cal arrays I get a BLOCK INPUT ERROR.

Some things of interest to note:

• I verify that after the learn string is restored, that the frequencies, number of points, and power level are correct
• After sending CALIS221, the frequencies, number of points, and power level have changed, (but only when it's misbehaving) .  Then if I send the cal arrays, I get the BLOCK INPUT ERROR, presumably because because I'm not sending enough data. 
• I tried checking the number of points after sending CALIS221, and fixing it if needed, and then sending the cal arrays.  It's an ugly Band-Aid, and the frequencies and power level are still incorrect.   I could apply more Band-Aids, but I want to get to the root of the issue. 
• This is intermittent.  It sometimes works, so I believe my code for getting the learn string, cal arrays, writing them to disk, and restoring them to the VNA are ok.
• This happens only on CALIS111 and CALIS221, sometimes.  It's fine on the full two port and on response cals all the time.

Is this a known issue?  Any suggestions for addressing this?

Any reason that CALIS221 would change the source parameters?

Thanks in advance,

Kathy