Cannot assign import route to Forestry Control Tower

Issue description

I cannot assign a unit storage holding tree saplings as an import route to a Forestry Control Tower. I'm not sure what else one might import there, and I'd really like my tree planters to stop traveling halfway across the map to get saplings.

Reproduction steps

1. Create a Forestry Control Tower
2. Create a Unit Storage and assign it to hold Tree Saplings
3. Click on the Forestry Control Tower
4. Click on the +/- button under Import Routes
5. Click on the Unit Storage
6. "Unit storage: Invalid route assigned" appears

Game version and build number

v0.6.3a (b333)

Operating system

Windows

Attachments

The real issue here appears to be that I cannot assign an import route from a storage with "keep full". That might make this "working as designed", I guess with the correct solution here being to use a second storage feeding into the one I want to import from.

Since I got the migration notice from GitHub to here, I'll provide some updates:

• The "real issue" comment was misleading
• You still cannot assign a unit storage containing saplings as an import route to a forestry control tower
• You can assign a fuel station as an an import route, and as far as I can tell, this is the only thing you can assign

Given the last bullet, I guess this is more of a feature request than a bug report.

It's not a bug. Build a second storage right next to the first one and export the saplings from it.