Composer dependency doesn't appear to update to latest version when plugin is updated to latest version

Description

I'm unable to get Craft to update a dependency properly. My Craft install currently has Sprout Base v1.0.5 installed and when I install a new plugin with the requirement of sprout-base ^1.0.0 it doesn't get updated and if I'm more specific in requiring sprout-base ^1.0.9` I get errors saying it's not found.

Version 1.0.9 appears to exist and be published:
https://packagist.org/packages/barrelstrength/sprout-base

I can run composer require barrelstrength/sprout-base from the command line and get back v1.0.9.

Steps to reproduce

1. Install Sprout Fields v3.0.0 via composer and make sure the version of Sprout Base that gets required along with it is v1.0.5
2. Update Sprout Fields to v3.0.3 via the plugin store (or whatever latest version)
3. Add a Phone field to your interface and leave it blank when you try to save.

Additional info

• Craft version: RC14 (? the latest)
• PHP version: 7.1
• Database driver & version: MySQL
• Plugins & versions: Sprout Fields, Sprout Reports, Sprout Base (yii module)

No source files or tests are named. Reproduce the Composer update flow using the listed Sprout Fields versions and the Craft plugin store, then trace how plugin dependency requirements are resolved. Done means Sprout Base updates to the available compatible version and the blank Phone field can be saved without errors.