A cache issue might be causing this unusual behavior. Let's try to do troubleshooting steps to fix this.
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2. Clear the browser’s cache to remove or delete the saved activities.
If you have questions you can comment below or post again. Have a good one!
Generally you do not ever want to post to that account. You should be posting to the appropriate expense account.
That account exists because QBs will allow you to turn off the Require Accounts Preference setting (not recommended). If you do that, then QBs will automatically use the Uncategorized Expense account.
Why were you trying to use this account? Maybe we can give you a better option.
Accountants and bookkeepers often use the Uncategorized Expense account when they need more information from a client about one or more expenses in order to assign them to the right accounts. Sometimes there are just a few uncategorized expenses while we've also seen clients with dozens or even hundreds (especially in a clean up situation). We built an app called Uncat on the QuickBooks App Store to help us get descriptions and receipts for expenses back from clients without having to export and email spreadsheets of uncategorized expenses back and forth. We hope it's useful to other bookkeepers and accountants.