When showing a konsole on beamer or in a web conference I often enlarge the font size by pressing CTRL-+ a few times.

When entering insert/leaving insert mode in Vim suddenly the original font size gets restored. I guess some special ESC sequence is causing this, but I don't know the exact reason.
This does not happen with a blank vim config, so it must be triggered by one plugins or configurations, but actually I don't know which one.

Maybe a developer has in idea what could cause this. For me it looks like a bug in konsole. If this restoring of the font size should is a "feature" that I'm not aware of it, maybe you can tell me how it works. Maybe it is then possible to work around it by changing some Vim config.