Looking at the plans grid (at wordpress.com/plans/example.com) I noticed several glitches related to the "Upgrade" action buttons. They are all visible in the screencast that's attached below.

1. The font size on the buttons changes when they become sticky. (All except the Downgrade button.) There is no reason for that, they continue to be exactly the same buttons. I understand why the labels change to include the price, that's because the price info has scrolled away, but I think no other changes are justified.
2. I was confused by the "Upgrade – €17" label. At first I read it as "minus €17", as a discount (and there actually is a discount there!), and only later I realized it's a "dash followed by the actual price". I think "Upgrade (€17)" would be a better label, ruling out the "minus" interpretation.
3. When I scroll up, then on the bottom edge of the page the action buttons also become sticky (or at least get the sticky styling), but they are not really sticky, they scroll away.