Error while Modify the Web Parts in SharePoint Page

I come across a strange error when I was trying to modify the web parts in a SharePoint page when I have not selected Edit Page from the Site Action Menu. The error says:

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Server Error in '/' Application.
The file is not checked out. You must first check out this document before making changes. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: Microsoft.SharePoint.WebPartPages.WebPartPageUserException: The file is not checked out. You must first check out this document before making changes.Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace:
[WebPartPageUserException: The file is not checked out. You must first check out this document before making changes.]
Microsoft.SharePoint.WebPartPages.SPWebPartManager.SaveSomeChanges(SPLayoutProperties layoutProperties) +1468
Microsoft.SharePoint.WebPartPages.WebPart.SaveSomeChanges(SPLayoutProperties layoutProperties) +82
Microsoft.SharePoint.WebPartPages.SPWebPartManager.WPSaveSomeChanges(SPLayoutProperties layoutProperties) +135
Microsoft.SharePoint.WebPartPages.SPWebPartManager.ApplyChangeList(String changeString) +721
Microsoft.SharePoint.WebPartPages.SPWebPartManager.OnLoad(EventArgs e) +712
System.Web.UI.Control.LoadRecursive() +101
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Control.LoadRecursive() +211
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2588

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Upon further trial I found a Web Part was there on the SharePoint page which was in Minimized state. So if I try to modify any web part in this page the above error comes. I restored this web part and then error has gone and I was able to Modify the other web parts in the page without everytime after doing Edit Page from the Site Action.

Strangely this works fine if click Edit the Page first and try to modify other web parts even when one web part on the page is in minimized state!!!

You can also find interesting to read Restoring Closed Web Parts and All Web Parts on a Page

Attempt a Question on WebParts: Question on Web Parts