Impress presentation layout change on upgrade from 5.2 to 5.3.

Some time ago I’ve upgraded LO from 5.2 to 5.3 on one of my computers. The presentation prepared in 5.2 (or earlier) suddenly changed its look in LO 5.3.

The original layout is presented on the first image, the new look on the second.

I’ve downgraded LO to 5.2 on this computer and the original layout was restored.

Is it a bug or something was changed in format itself or in its interpretation in Impress?

With Regards,