The hosted workbench restores your web parts on the next site you open in the same tab
The hosted workbench (/_layouts/15/workbench.aspx) stores its canvas in sessionStorage under sp_webpart_workbench_state — without you pressing Save, and keyed by the tenant origin, not by the site. Open the workbench of another site in the same tab and the web parts you added before are restored and boot there, with the new site's pageContext. If your web part provisions lists on first run, it now does so on the wrong site. Clear the key (or remove the web part from the canvas, or open a fresh tab — not a duplicated one) before switching sites.
Hostovaný workbench si plátno drží v sessionStorage pod klíčem sp_webpart_workbench_state – bez uložení a pro celý tenant, ne pro web. Když v téže kartě otevřeš workbench jiného webu, vložené webparty se obnoví a spustí s pageContext NOVÉHO webu. Webpart, který při prvním spuštění zakládá listy, je založí na cizím webu. Před přechodem na jiný web klíč smaž (nebo webpart z plátna odeber, případně otevři novou kartu – ne duplikovanou, ta si sessionStorage kopíruje).
Symptom
You use the hosted workbench to check a web part's property pane or toolbox entry on a real site — a good place for it, because nothing is saved to a page.
Then, in the same tab, you open /_layouts/15/workbench.aspx on a different site to check another web part. The canvas is not empty: the web part from the first site is already there, it starts, and it shows its first-run state ("Preparing the app for first use – creating lists"). A few seconds later the second site has new lists that belong to an app that is not installed there.
Cause
- The workbench serialises the canvas into
sessionStorage['sp_webpart_workbench_state']as you add web parts. It does not wait for Save. sessionStorageis scoped to the origin (https://<tenant>.sharepoint.com) and the tab — every site in the tenant shares it.- On load, the workbench restores that state on whatever site it is opened on. The restored web part gets the current site's
pageContext.web. - A "first run" gate kept in
localStorageper site URL does not stop it: on the new site the gate has never been set, so provisioning runs.
Fix
Before you navigate to another site's workbench in the same tab:
sessionStorage.removeItem('sp_webpart_workbench_state');Or delete the web part from the canvas, or open the other site in a fresh tab you start yourself (typed URL or bookmark) — a duplicated tab copies sessionStorage, so it carries the canvas along.
If it has already happened:
- Leave the page so the web part stops.
- List what was created in the last hour and check it is yours and empty:
GET /_api/web/lists?$select=Title,Created,ItemCount&$filter=Created ge datetime'2026-11-14T00:00:00Z' - Only lists with
ItemCount = 0that were created by that run go to the recycle bin (POST /_api/web/lists(guid'…')/recycle()), not permanent deletion. - Check anything else first-run provisioning touches (a central registry list, site columns, permissions).
Related
- Provisioning that runs on every load is a separate trap; gate it, but remember the gate is per site.