Preview corrupts tag (or tag sequence)

It often happens that somebody posts a reply while I'm typing one. At the moment I hit the 'post' button I'm redirected to the preview. Fine.

But this preview screws up tags, specifically something like

Type [b][nobbc][code][/b][/nobbc]
Paste your code after that
Type [b][nobbc][/code][/b][/nobbc] after that

Don't have an example what it looks like but it's a mess :wink:

Please let a preview be an exact replication of what was typed.

Windows 8, Firefox 50.1.0

Thanks in advance.