Merge branch 'master' into blender2.8

source/blender/editors/interface/interface_utils.c

@@ -462,6 +462,17 @@ uiButStore *UI_butstore_create(uiBlock *block)
 
 void UI_butstore_free(uiBlock *block, uiButStore *bs_handle)
 {
+	/* Workaround for button store being moved into new block,
+	 * which then can't use the previous buttons state ('ui_but_update_from_old_block' fails to find a match),
+	 * keeping the active button in the old block holding a reference to the button-state in the new block: see T49034.
+	 *
+	 * Ideally we would manage moving the 'uiButStore', keeping a correct state.
+	 * All things considered this is the most straightforward fix - Campbell.
+	 */
+	if (block != bs_handle->block && bs_handle->block != NULL) {
+		block = bs_handle->block;
+	}
+
 	BLI_freelistN(&bs_handle->items);
 	BLI_remlink(&block->butstore, bs_handle);