Display problem on the ajax when you choose a type of activity with a textarea custom field

When tinymce is active, and a type of activity contains a custom field textarea the ajax blob doesn't include all the mandatory tinymce includes).

Step to reproduce (on a local server, in firefox:

activate tinymce, create a new type of activity "test", add a custom field textarea/note test on a group associated to the custom activity test.

(assuming the test activity type == 42

localhost/civicrm/contact/view/activity?atype=42&action=add&reset=1&context=standalone

the normal activity is going to be displayed, then the custom fields for the type 12 are going to be loaded and it will generate an empty screen loading endlessly.

If you use opera, it works fine. if you are in debug step by step on FF, it works fine too (beside a lot of js error messages about tinymce stuff missing).

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