Comprehensive problem

Would you please explain grammar of this sentence? I am confused about "as" in this sentence.

Strange as this behaviour may be , there is a very good reason for it.

Solution 1:

Swan in Practical English Usage (p72) has an explanation for this construction in the section 'as and though: special word order':

As and though can be used in a special structure after an adjective, adverb or noun. In this case they both mean 'although', and suggest an emphatic contrast. (In AmE only as is normally used like this; though is unusual.)

• Cold as/though it was, we went out. (= Although it was very cold,...)
• Strange though it may seem, I don't like watching cricket.

So the sentence Strange as this behaviour may be, there is a very good reason for it can be understood as:

• Although this behaviour may be strange, there is a good reason for it.