PHP Warning: Invalid Argument supplied for foreach() in lessc.inc.php on line 774

I'm running the module with a file that's parsed without errors by LESS.app and produces working CSS. However, whenever my CSS files are rebuilt from the LESS file - on every page load in development mode. I get several (17) warnings:

warning: Invalid argument supplied for foreach() in /var/www/modules/less/lessphp/lessc.inc.php on line 774.

Line 774 to 779 of the above-mentioned reads:

					foreach ($value['__tags'] as $innerTag) {
						$visitedMixins[$innerTag] = true; // prevent rendering this block multiple times
						$new_tags[] = trim($outerTag.
							($innerTag{0} == $this->selfSelector || $innerTag{0} == ':'
								? ltrim($innerTag, $this->selfSelector) : ' '.$innerTag));
					}

I've had a look at my mixins - specifically I've removed references to CSS3PIE, tried URLs with and without quotes, and checked that my parameters are defined correctly. All mixins only one parameter.

Can I safely ignore this warning?