Hi Andrew,
I think you might be hitting this bug;
CSCee44462 Bug Details
Headline Need ability to generate inband test tone on 7941/61/70/71 like 7960
First Found-in Version 8.0(3), 5.0(1)
Status Assigned
Symptoms:
7941/61/70/71 phones cannot generate 1004Hz -15dB test tones the way a 7960 is capable of doing.
Conditions:
Any network where 7941/61/70/71 phones are being used and a test tone is needed to troubleshoot a loss plan or echo problem.
Workaround: Use the test tone on a 7940 or 7960.
Hope this helps! Sorry man.
Rob