Using Edit > Insert > Peptides, insert peptides increasing by 1000 AAs from 1000, 2000, 3000, etc.
Hover the mouse over each in turn pressing the down and up arrow keys to test for responsiveness to the keyboard for selection change.

You should see that above 2000 (e.g. 3000 and higher) there is significant "hang" before the UI begins responding to the keyboard as it tries to display the normal Windows Tree control tip with the text in the node you are hovering over.

We should probably choose a reasonable length to show an ellipsis "..." and then improve our own yellow tip in this case to display the entire sequence, which we already have working for FASTA-backed nodes in the Targets tree.