You can't change the title of a page by adding or removing a
semicolon, or whatever character that is ignored in the structure name.
As a workaround you change the title in two steps by making an extra
change in the first step and remove that again in the second step.
Okay, this has been finally fixed. Also the tests have been enhanced to
catch this case. Will be published with the other patches, fixes and
enhancements to public StORE soon.