"Execute SQL...(F9)" grayed out and does not work in random circumstances

Hi,
when I work with my data, I usually have multiple query tabs open. In the recent build (3734) it occurs to me very often that after a query tab has been used to launch a query (i.e. by pushing the Play button or F9 for execution), the same query window cannot be used for another query. Instead I have to close it and reopen a new tab. This problem does not occur every time, but it persists in the sense that happens to me several times every working day.
Thanks,
Steve

Same as here.