|ImportTransitionListColumnSelectDlg lags a bit when associate proteins checked
If you use the SkylineTester - Forms tab to bring up the ImportTransitionListColumnSelectDlg, and then check the associate proteins checkbox, it can take seconds before it is clear the click made an impact. I assume the code is attempting to associate proteins for all of the peptides in the list. It may also be associating every row using a separate lookup. There should be a map based on the bare (unmodified) peptide sequence to avoid duplicating lookups, and at this stage, all that needs to happen is association of the rows the form is showing, which is probably less than 20 peptides and should not take that long.
Finally, it may be worth protecting this with a LongWaitDlg so that in case it does take a while the user sees progress instead of fealing that the click may have not registered.