Dynamic map calculation very slow with additional parameters (precomputing every possible combination?)

[VolkerH]

Issueing a ticket for an issue I mentioned on gitter (on May 3 2018).
The noteboook at
https://github.com/VolkerH/my_hv_gallery/blob/master/Images_with_interactors/Dynamic_map_interactor.ipynb
demonstrates the issue.
The upper cell creates a dynamic map which lets the user slice through a volumetric time series using T,Z sliders. This works fine.
The lower code adds a few lines of code which add additional parameters vmin, vmax that should control the intensity range. If the range of vmin, vmax is large, the figure is not shown in a reasonable time. When reducing the ranges of vmin, vmax to a few values it works again. It appears that under the hood something gets pre-computed for every possible value combination of the sliders (which combinatorially quickly becomes very large).