Mazda: rear window panel for miata, sorry andy, warm weather

Question
I recently had a new back window panel installed in my 1995 Miata.  It seem to work ok for a week or so, it would zip ok when I did not have it latched fully.  Now I cannot get it zipped fully without unlaching the top.  But when I get it zipped I cannot relatch the top.  The cover will not stretch.  I live in Phoenix and it was warmer when I had it installed.  I am guessing the top stretched easier in warm weather.  What do you think?

Answer
Dear Michael,
Thank you for your enquiry.
Was this a genuine Mazda part? - from the Mazda factory!
There are many imitations about, some are OK but others are just not as good as the real thing.
They are temperature sensitive, and your theory may well be correct.
Is the part fitted the same as the original?
The originals were a plastic that you had to be careful to fold. Many replacements are a thicker perspex that will not bend. - much better.
I can't think of anything else.
sorry.
Andy