Getting loads of these: uncaught exception: 2152071170 7 calStorageCalendar.js:1736:7

https://searchfox.org/comm-central/rev/c0fb2575fb46e9036dcf758c4f3962035616602a/calendar/providers/storage/calStorageCalendar.js#1736

Exception { name: "NS_ERROR_OBJECT_IS_IMMUTABLE", message: "Can not modify immutable data container'Can not modify immutable data container' when calling method: [calIItemBase::recurrenceInfo]", result: 2152071170, filename: "file:///home/magnus/Code/tb/mozilla/obj-x86_64-pc-linux-gnu/dist/bin/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/components/calStorageCalendar.js", lineNumber: 1736, columnNumber: 0, data: null, stack: "_assureRecurringItemCaches/<@file:///home/magnus/Code/tb/mozilla/obj-x86_64-pc-linux-gnu/dist/bin/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/components/calStorageCalendar.js:1736:7\nhandleResultInner@file:///home/magnus/Code/tb/mozilla/obj-x86_64-pc-linux-gnu/dist/bin/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/components/calStorageCalendar.js:272:21\nhandleResult@file:///home/magnus/Code/tb/mozilla/obj-x86_64-pc-linux-gnu/dist/bin/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/components/calStorageCalendar.js:266:41\n", location: XPCWrappedNative_NoHelper }

Pretty sure this is from bug 501689 since it just started.
Not sure exactly what the consequences are.

Based on the line number this might be fixed with https://bugzilla.mozilla.org/attachment.cgi?id=9093466&action=diff

Looks like it, thx Stefan!