Loading old maps in snapshot breaks the signs

I had this happen to me in 15w31a, only in the Nether, and then not afterwards. I've currently been through snapshots since then up to 15w35a without incident. Signs in the Overworld were not affected. Weird.

EDIT: By loading my world in each snapshot upgrading 1 at a time, the issue is no longer there. However, empty lines are replaced with null starting with 15w32c.

Having the same issue:
1.8.8:

15w34b:

Was this map loaded in 15w31a? If so signs were corrupted in that snapshot.

I'm not sure how this is a duplicate, one is about empty lines becoming "null" and this is about only the first word of a line actually being visible.

It's also still not fixed, whereas that bug is closed and fixed.

Cannot reproduce when updating a 1.8.x world in something > 15w33c.
When the world was loaded in an earlier 15wXX snapshot, then the signs are destroyed.

Please provide exact steps to reproduce.

The map that I'm loading is a map I made in 14w20a.

Steps:
Make a map with a sign in 14w20a
Load the map in 15w35b
Only the first word of each line is displayed

If you want a download to the world

14w20a is unsupported. Does this also happen when upgrading from release versions such as 1.8.8?

It used to, but 14w20a -> 1.8.8 -> 15w35b works now.

Thanks.