Hello. I want to put an icon into the document form, which represents current document status - posted, deleted and some else. Everything is OK with statuses "posted/not posted" - I can create status icon (as form attribute) when the event oncreateatserver occurred and i can upd ate it when document posted/unposted in afterwrite event. But with deletion mark it doesn't work - I cannot find and event which occurred when deletion mark is se t in the document form object. Is there any such event? Maybe there exists any other way to do this?

You will have to disable standard commands for deletion mark setting/clearing and provide your own commands as a replacement, this will allow you to handle the deletion mark change event.

How can I disable standard command for deletion mark without rebuilding command bars in all document forms?
And another question - Can this behavior be considered as a platform bug?

Yes, you need to rebuild the command bar for the document form. Not for list or choice form as you need only to catch a moment when the deletion mark is changed for the opened document form. Other cases of deletion mark change you will handle in the OnCreateAtServer handler.