Popup does not correspond to the first visible item in the RecyclerView

[primalbet]

using the scrollbar, the current item that is shown in the popup is NOT the item at the top of the list. Example:

https://gyazo.com/48bf09b1bdffa3bfcc8aa1d87a39a79f

the M is the 4th item from the top of the list instead, it should show L because that is the first item at the top.

[AndroidDeveloperLB]

Actually I can see it on the sample too. Sometimes the header text is shown, and sometimes the item, and the text many times doesn't match what's on the first one that's shown.

See:

w5O2UMjBDK.zip