Hi William,
Thanks for using Syncfusion products.
We have analyzed the reported issue (Maskedit post value gets lost on repeated post backs) with sample in 13.1.0.30 version and able to reproduce the issue in our end. We have confirmed this as a defect and have logged an issue report regarding this. A support incident to track the status of this defect has been created under your account. Please log on to our support website to check for further updates.
https://www.syncfusion.com/account/login?ReturnUrl=%2fsupport%2fdirecttrac%2fincidents
Please let us know if you need further assistance.
Regards,
Saranya.S