MT4 hangs when switching TF with EA on

When I leave an EA on and forget to switch it off (first), when I switch timeframes or try closing the program the whole thing hangs. I gotta switch TFs with the EA button off.

Is this a problem with the EA itself, or with MT4?

without seeing the EA code not easy to tell at all but most likely to be the EA.

You can check by trying any other EA and switching tf it should work fine.

Here is a quote from sources unknown (sorry to the writer for not being able to name you):

"Changing timeframe or currency runs deinit() and init() and resets all the externs but does not change static values and does not change global variables."

So an EA needs to be designed to allow for this event else the result will be unpredicatable.
It is no surprise that your system hangs.