Index: core/units/helpers/image_helper.php
===================================================================
--- core/units/helpers/image_helper.php
+++ core/units/helpers/image_helper.php
@@ -124,6 +124,13 @@
 					$src_path_escaped = preg_replace('/(\\\[\d]+)/', '\\\\\1', $src_path); // escape replacement patterns, like "\<number>"
 					$dst_image = preg_replace('/^'.preg_quote($src_path, '/').'(.*)\.(.*)$/', $src_path_escaped . DIRECTORY_SEPARATOR . 'resized\\1_' . crc32(serialize($params)) . '.\\2', $src_image);
 
+					// Keep resized version of theme-based images under "system" folder.
+					$theme_path = $this->Application->GetFrontThemePath();
+
+					if ( preg_match('/^' . preg_quote(FULL_PATH . $theme_path, '/') . '(.*)$/', $dst_image, $regs) ) {
+						$dst_image = WRITEABLE . $theme_path . $regs[1];
+					}
+
 					$this->fileHelper->CheckFolder( dirname($dst_image) );
 
 					if (!file_exists($dst_image) || filemtime($src_image) > filemtime($dst_image)) {