Question: Maple 2020 cannot work with a .mw file created in 2006--any workaround?

Example of problematic file:  Model050913.mw

Maple 2020 (either 32- or 64-bit), Maple 2019, and Maple 2017 cannot open a .mw file that I created in 2006.  These Maple versions display this .mw file from 2006 as a garbled mess and cannot work with the garbled mess.  In contrast, Maple 18 opens this file from 2006 without problems.  Did the .mw file format change some time after Maple 18?  Interestingly, Maple 2020 can open a .mw version of the problematic 2006 file that I save with Maple 18.  Can Maple 2020 be updated so that Maple 2020 can open old .mw files (e.g., 2006 and earlier)?  Is the inability of Maple 2020 to open files from 2006 and earlier a bug in Maple 2020?  I can workaround this problem by using Maple 18.  But correcting a bug in Maple 2020 that garbles old .mw files would be helpful.