This is an exception edge case which could happen a bit more often than expected.
steps to reproduce:
1) active the Pain Inventory survey
2) login to the MyOSCAR portal and start the Pain Inventory survey
3) select 0, click next
4) select 1, click next
5) select 2, click next
6) select 3, click next
7) select 4, click next
8) select 5, click next
9) select 6, click next
10) click the magnifying glass to view this completed survey
11) click ok to the prompt about the read-only viewing
12) click back 6 times to get back to question 1
13) change question 1's answer from 0 to 10
14) click next
15) click surveys
16) click the magnifying glass to view this completed survey
17) click ok to the prompt about the read-only viewing
You will land on question 2 with no answer selected. If you select a number and click next, the following question is blank too.
the more general description for this bug should be that MUMPS surveys do not lock completed surveys.