[triceratops]

You're right if the land is sold at market price. If it's sold at a discount because of the restrictions, then continuing to enforce those restrictions is valid. The land's value is permanently reduced due to the inability to build, and the price reflects that.

[Dylan16807]

The price only reflects the future value out so far. The market price is based on a small number of decades. So for the purpose of respecting the discount, that reason dries up after a while.

[_heimdall]

Stipulating that such contract must expire after a period of time seems more reasonable than saying such a contract isn't valid at all.

[triceratops]

So add a time-limit to the restriction.