Terrain difficulty not preventing units from moving?

[fire-eggs]

Units such as a diplomat or calvary seem to be able to move onto terrain at all times. Specifically, they seem to always be able to move into mountains.

In Microprose CIV, a unit might fail to move into mountains, even when they have full movement available to them.

[EnockNitti]

An observation I have made in CIV1 is that, if the diplomat or cavalry, only have one movement point when trying to move to a mountain the almost always succeeds. Assume this is a bug that should not be reproduced in CIVONE.