Legacy XhtmlConformance Kills Partial Page Updates
Sys.WebForms has no properties
Sys.WebForms.PageRequestManager is null or not an object
In my case, the innocuous-looking
Sys.WebForms.PageRequestManager.getInstance() was causing the latter. A big thank-you goes to Stefan Goßner and Scott
Guthrie for pointing out how to fix this predicament and get partial rendering back:
These empirical, anecdotal edge cases make me want to scream.