Before committing D3621, I was checking if ID handling is working properly.
I found this issue.
During debugging in MSVC (probably not up to date version), debugger was confused about Sequence type.
this was due to line in BKE_sequencer.h:
typedef struct Sequence *(*SeqLoadFunc)(struct bContext *, ListBase *, struct SeqLoadInfo *);
When I reformated this it was OK. Should I fix this, or is it bug in MSVC?