<zk>
<grid width="60ex">
<columns>
<column label="Arabic numeral" />
<column label="Capital letter" visible="false" />
<column label="Roman numeral" />
</columns>
<rows>
<row>
<cell><label value="1" /></cell>
<cell><label value="A" /></cell>
<cell><label value="I" /></cell>
</row>
</rows>
</grid>
<separator />
<grid width="60ex">
<columns>
<column label="Arabic numeral" />
<column label="Capital letter" visible="false" />
<column label="Roman numeral" />
</columns>
<rows>
<row>
<cell><label value="1" /></cell>
<cell style="white-space: nowrap;"><label value="A" /></cell>
<cell><label value="I" /></cell>
</row>
</rows>
</grid>
</zk>

The first Grid shows a correct result. The second column is configured as not visible and in fact you see neither the column label nor the column content.

The second Grid shows the bug. The second column is configured as not visible and, in the corresponding Cell, a Style is added. Now you don't see the column label (correct), but the visible column content is the wrong one.
Watching the produced HTML, it shows that the two styles (the Column one and the Cell one) are not properly merged.