By default, the highlighted color of the execute statement does not have high contrast to differentiate from other statements in the window. I like light green color to show which is the execute statement. So I changed the foreground to that color in the preferences. Since then, I noticed the following symptoms:
A. Some times, the execute statement has the green color selected and runs as I expected.
B. Some other times, the execute statement disappears and then appears with no highlight and with no update in the output window. The cursor turns to hour-glass. This stays that way until the execution completes. Then everything is normal.