Steps to reproduce:
1) Make 2 docs, sub1.odt and sub2.odt, inserting a little text, anything will do
2) Make master doc master.odm
3) add sub1 and sub2 as links to master using Navigator
4) in Navigator, choose Edit Link and uncheck sub1 and sub2's  Write Protection > Protected check
5) save master.odm
6) in master LOWriter window, modify the sub1.odt text (there is no warning)
7) save master.odm
8) close everything
9) reopen master.odm
10) say yes to "update links" 

Observed behaviour:
a) the modifications made at point 6 have been lost, and 
b) the file timestamps indicate that only master.odm has been saved.

Expected behaviour, one of the following:
A) Preferred, as this is the most useful: All modified sub-files are saved and the master not since it is unchanged. If you skip the save at point 5, both master and sub1 should be saved.
B) Safe but not very satisfactory IMO: Make it impossible to remove the link write-protection feature
C) Silly as it is functionally equivalent to B) IMO, but still better than time-wasting human work loss: A warning pops up, saying "this will not be saved"