Sigil 1.2.0 Undo Issues

I've got Sigil 1.2.0 on Linux. Brilliant software. Just one question. I sometimes run into a situation where I need to undo an action, where Sigil undo (ctrl z) is unresponsive.

I find that undo works for individual text edits within a page, but any structural edits, and bulk find/replace edits, basically anything other than typed text within a page, wouldn't respond to undo. I have search the forum for clues, but couldn't find any, so please forgive me if I'm posting about a known issue.

I cannot tell weather this has got something to do with my build (from source), my system configuration, QT5, or what. Any help or advice will be great.

Thanks!