Numbering does not work right

[Erik]

I have a document with chapter headings in 3, sometimes 4 levels.
it goes something like this:
1 Heading1
A Heading2
B Heading2
C Heading2
2 Heading1
A Heading2
B Heading2
C Heading2
3 Heading1
I Heading2a
II Heading2a
III Hwading2a
4 Heading1
a Heading2b
b Heading2b

etc
The numbering of levels 2, 3 and 4 is different.
It's because each chapter was written by a different author and the
document is a collection of those articles
Now the numbering of levels 2, 3 and 4 some times does not start at
1, A or I, but seems to continue over the Heading1-levels like this:

1 Heading1
A Heading2
B Heading2
C Heading2
2 Heading1
D Heading2 <== but i set it to start at A !!
E Heading2
F Heading2
3 Heading1
I Heading2a
II Heading2a
III Hwading2a
4 Heading1
IV Heading2b <== but i set it to start at I !!
V Heading2b

etc
in Chapter 2, level 2 does not start at A, but I have set it so it
should do it.
WHat I do is set it right (to A) then it does not show it does, then I
do a Control-Z and then it is indeed set to A.
Later on, I do not know when and why, it is set back to D, magically.
it flips back to D.

What is happening here ?
What do I do wrong ?
Anyone ever seen this ?
Can anybody help ?