Units stuck at trees on Extinct Volcano

[elexis]

Since the bumps on extinct volcano can sometimes be very steep, these trees might become inaccessible.

This is an r19686 replay provided by cc showing the bug.

It's not easy to resolve if we want a sufficient amount of both hills and lower areas simultaneously.

[FeXoR]

Would adding ramps to low ground help? The direction of the ramps might still be tricky to chose.