Yes, it is weird. But it true.
What really astonishes me, is that this is the case in the whole western world as far as I know.
I guess it is because the Muslims are poor in those countries and the communists IMO have problems to use their brains correctly.
Communists tend to sympathize with anyone they view as oppressed, unless the opressed people are being oppressed by a communist regime, then they hypocritically ignore it, or openly support it, denying the fact it's oppression.
I've noticed many communists for instance are actually anti-Tibetan independance; the only reason I could ponder this is because Tibetan independance would mean them being independant from a communist regime. But, only adding to the confusion, the Dalai Lama has expressed Marxist views...so I really don't know about that.
They are also of course vehemently opposed to nationalism, so they'd be opposed to Zionism, even though neither party in the middle eastern conflict is communistic. For the Muslims it's all religious for the Zionists it's nationalism and religious (sometimes more to the former only as there are secular and cultural Zionists; and, of course, people who simply support their country).
In truth, this weird Muslim-Communist alliance is a temporary one at best. Much like the Nazi-Japanese alliance in World War II, in the event they were to win the war, they'd eventually fight each other.