Show hidden files in the solution folder in Windows Explorer, and you will find the visual studio * .suo file (it contains information related to the user). Delete it, after opening the solution the next time it will be recreated. It seems that sometimes there are problems with this file (for example, you take this file from another user computer through a control source (by the way: DO NOT PUT THIS INTO SOURCE MANAGEMENT!)); this leads not only to “not opening previous tabs”, but also to other confusing things, since it is not possible to save the “launch” project between restarts of the visual studio.
Even a typical .ignore file for source control suggests NOT to add it:
[Bb]in *.user *.suo *.[Cc]ache *.bak *.ncb *.log *.pdb *.DS_Store [Tt]humbs.db _ReSharper.* *.resharper Ankh.NoLoad
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