So what do you think, when scope´s freezes while adjusting vertical line, is it a bug most scopes then got ?
Keysight are mentioned not to do this, also GWInstek - Not all models.
Keysight does, even their new MXR. But much more responsive than its competitors - Keysight is always superb at.
I think all digital scopes will display history waveform rather than acquire in real time when adjusting. It's a matter of current time base setting, memory depth and the instruments' processing power. Almost all scopes will freeze at large time base or large memory depth, in which situation it's too hard to process in real time.
Some scopes choose to reacquire until adjusting is done, no matter what current settings are, so they "freeze". Maybe it's a limitation of the hardware, they can't refresh in time so it will make the scope slack if reacquiring-while-adjusting, or it's just a software issue to be optimize, who knows.
Some scopes, like Keysight, choose to periodic reacquire while adjusting at smaller time base or memory depth, so the displayed waveform flickers rather than freezes. Keysight scopes behave more like a analog one which is always welcomed.