If you just harvested a crop, the info about the loot you receive can block the selection of the next crop you want to select. This mainly affects the top row of the seed selection menu. I assume this is mostly an issue with mouse.
Steps to Reproduce
1. Harvest previous crops
2. Try to plant a new seed with mouse and notice the top row is impossible to plant
A developer has marked this issue as fixed. This means that the issue has been addressed in the current development build and will likely be in the next update.