Variations issue on product page

The product page does show more Variations than programmed if there are more than one characterictics on the same product page.

for example: you have three characteristics for the same product. But not all combinations are for use.
Even if you have made the right selection on the Variation page you still can make any combination on the product page at the front end even it the combination was NOT in the variations available.

example

variation 1. length= 3, color= green, size= 45
variation 2. length= 3, color= black, size= 50
variation 3. length= 4, color= black, size= 45

characteristics

length ,4
color= green, black
size= 45,50

the selection of length= 4, color= green, size= 50 is selectable even if there was no variation made for it!

That's indeed the case. The dropdowns have to show you all the values, otherwise, you wouldn't be able to select all your variants.
However, even though you can select it, you won't be able to buy it because that will be detected by the system and the add to cart button should not be displayed.